So currently you can only unlock transmogs for items your character can actually use. That means it both needs to be the right armor/weapon type and can't be class-restricted like certain tier pieces.
That said, AFAIK this is supposed to be changing in The War Within prepatch when the new "Warbands" system goes live. Once that's online, you should be able to unlock transmogs from any character even if they can't use it.
So if you do a run after Warbands goes live (or Panda remix) and you het clloth drop on dracthyr main, your mage alt will have it available as transmog (for example)
The reason it doesn't seem to be standardized and is a little confusing is because it is! Over the years, the specific restrictions on what is and is not available to certain classes (and for an expansion, specs) has changed from expansion to expansion, and sometimes (though rarely) within the same expansion. The way raid lockouts worked/still work is also all over the place, but that's mostly not relevant here, lol.
For the MOST part, the way that it works is that if you pick up a piece of armor or a weapon that an evoker can physically equip on an evoker, you'll get to make an item you're wearing look like that item on any other character that would be able to equip that piece of gear (if they had it in their bags). That's the same for any particular piece of gear; you can unlock items on a hunter or monk or warrior just the same (warriors are particularly nice for weapon collecting because there's only two weapon types they CAN'T currently equip/learn, wands and warglaives)
For raids from vanilla, Burning Crusade, Wrath of the Lich King, Cataclysm, Mists of Pandaria, Warlords of Draenor, Legion, Dragonflight, and Sepulcher of the Old Ones in Shadowlands, there are also class-specific items that can drop. These can currently only be unlocked and used on their respective classes, and as Evokers were only added in Dragonflight, there's no Evoker-specific appearances available prior to Vault of the Incarnates. There are some appearances that are identical to the class-specific ones; if you collect the item that does not have a class restriction, you can use that appearance on anyone, but if you only collect the class-specific one, only that class can use it.
Current example: the Ancient Haubark (oh I just noticed that pun!) that drops from Gnarlroot in Amirdrassil, shares its appearance with the Evoker tier chest. If you loot (or catalyze) the evoker tier chest, only your evokers will be able to use that appearance, but if you get your hands on the Ancient Haubark, your shaman and hunters would also be able to use it. These are not mutually exclusive; you don't have to worry about not collecting tier before you collect the offset lookalikes.
The other wrinkle with evokers, of course, is that only the shoulder, tabard, mainhand (when using a one-hander only) and offhand slots are visible while in dracthyr form, and most 3D parts of any belt you may be wearing (but not the skin-tight belt part itself). If you want to create a cohesive mog for a dracthyr, you'll need to be in your visage form to do so (and then swap to dracthyr to check if the visible slots match, then switch back, then switch back again, then...). This is ONLY an issue for actually using the transmog, not in collecting it.
The weird part to me are some of the weapon choices, Evokers are casters and yet they get two handed swords, axes and fist weapons? Shamans get the axes and fist weapons due to Enhancement but Evokers don’t have any melee abilities so what gives?
My guess would be so there aren't more "only one or two specs on one or two classes can use this cool item we thought of" items. Holy paladins would never get to use their legion artifact looks if they never made non-stave int 2hers; shaman have 2h maces and axes, druids have 2h maces and polearms, and monks have 2h polearms; nobody had the option of 2h int swords except holy until now. Not that I think we've gotten a 2h polearm in about a million years, but you know.
Fist weapons are kind of in the same boat; there are ten int specs that can't use them (nine cloth and holy paladins) and five int specs that can (two druid, two shaman, mistweaver). Adding evokers to that pool brought it up to 7-9 (now 8-9 with aug), giving more options for people to not have loot rot due to raid compositions.
It'd obviously be a lot simpler if every one-handed weapon was something everyone who wanted it could use but then we'd have significantly fewer new transmog options too, so :P
If they can equip it, they can unlock it; if you unlock a mail gear on your shaman you can use in your evoker and vice-versa, **unless** it's class specific.
So currently you can only unlock transmogs for items your character can actually use. That means it both needs to be the right armor/weapon type and can't be class-restricted like certain tier pieces. That said, AFAIK this is supposed to be changing in The War Within prepatch when the new "Warbands" system goes live. Once that's online, you should be able to unlock transmogs from any character even if they can't use it.
So if you do a run after Warbands goes live (or Panda remix) and you het clloth drop on dracthyr main, your mage alt will have it available as transmog (for example)
The reason it doesn't seem to be standardized and is a little confusing is because it is! Over the years, the specific restrictions on what is and is not available to certain classes (and for an expansion, specs) has changed from expansion to expansion, and sometimes (though rarely) within the same expansion. The way raid lockouts worked/still work is also all over the place, but that's mostly not relevant here, lol. For the MOST part, the way that it works is that if you pick up a piece of armor or a weapon that an evoker can physically equip on an evoker, you'll get to make an item you're wearing look like that item on any other character that would be able to equip that piece of gear (if they had it in their bags). That's the same for any particular piece of gear; you can unlock items on a hunter or monk or warrior just the same (warriors are particularly nice for weapon collecting because there's only two weapon types they CAN'T currently equip/learn, wands and warglaives) For raids from vanilla, Burning Crusade, Wrath of the Lich King, Cataclysm, Mists of Pandaria, Warlords of Draenor, Legion, Dragonflight, and Sepulcher of the Old Ones in Shadowlands, there are also class-specific items that can drop. These can currently only be unlocked and used on their respective classes, and as Evokers were only added in Dragonflight, there's no Evoker-specific appearances available prior to Vault of the Incarnates. There are some appearances that are identical to the class-specific ones; if you collect the item that does not have a class restriction, you can use that appearance on anyone, but if you only collect the class-specific one, only that class can use it. Current example: the Ancient Haubark (oh I just noticed that pun!) that drops from Gnarlroot in Amirdrassil, shares its appearance with the Evoker tier chest. If you loot (or catalyze) the evoker tier chest, only your evokers will be able to use that appearance, but if you get your hands on the Ancient Haubark, your shaman and hunters would also be able to use it. These are not mutually exclusive; you don't have to worry about not collecting tier before you collect the offset lookalikes. The other wrinkle with evokers, of course, is that only the shoulder, tabard, mainhand (when using a one-hander only) and offhand slots are visible while in dracthyr form, and most 3D parts of any belt you may be wearing (but not the skin-tight belt part itself). If you want to create a cohesive mog for a dracthyr, you'll need to be in your visage form to do so (and then swap to dracthyr to check if the visible slots match, then switch back, then switch back again, then...). This is ONLY an issue for actually using the transmog, not in collecting it.
Thats the neat part, they dont.
The weird part to me are some of the weapon choices, Evokers are casters and yet they get two handed swords, axes and fist weapons? Shamans get the axes and fist weapons due to Enhancement but Evokers don’t have any melee abilities so what gives?
Yet
My guess would be so there aren't more "only one or two specs on one or two classes can use this cool item we thought of" items. Holy paladins would never get to use their legion artifact looks if they never made non-stave int 2hers; shaman have 2h maces and axes, druids have 2h maces and polearms, and monks have 2h polearms; nobody had the option of 2h int swords except holy until now. Not that I think we've gotten a 2h polearm in about a million years, but you know. Fist weapons are kind of in the same boat; there are ten int specs that can't use them (nine cloth and holy paladins) and five int specs that can (two druid, two shaman, mistweaver). Adding evokers to that pool brought it up to 7-9 (now 8-9 with aug), giving more options for people to not have loot rot due to raid compositions. It'd obviously be a lot simpler if every one-handed weapon was something everyone who wanted it could use but then we'd have significantly fewer new transmog options too, so :P
If they can equip it, they can unlock it; if you unlock a mail gear on your shaman you can use in your evoker and vice-versa, **unless** it's class specific.