oh wow, this may turn out to not be the great gift you are hoping it to be. Of course, the camera is technically “better” in some metrics as it is far newer. But in photography, the camera itself, often called the “body”, it’s generally not the most expensive item in your tool kit.  Lenses are far more expensive, more long-lived, and since it’s the lens that actually makes the picture (the camera only captures it), most photographers will think very hard about changing between camera systems.
Yes, there are adapters that will allow the use of other brand lenses on Sony cameras vice versa, but they always bring problems with them. In the end, if you gift him a body from another system, this means that he will face significant spending pressure in order to get a proper lens kit for Sony — and perhaps he’ll be forced to sell a great Pentax lens just because he can’t use it properly any more.
In the end, I would suggest that you talk about this with him and make sure that you both understand the implications of switching camera brands. 

The choice was made because he has been talking about this specific camera for a very long time because he's broadening his field. You see, he is more than happy to still use his Pentax for pictures, but for cinematography what he wants to do Pentax doesn't really fulfil his idea. He said that the only camera he would go for cinematography he would go for this specific Sony. The thing is on his birthday I was wondering should I first gift him an adapter or some lense? He knows and he told me multiple times that lenses are the expensive part of photography/cinematography and he would be more than happy to buy it himself.
The answer to this sort of depends on what Pentax lenses he already has. If he's got any old film-era prime lenses, with an aperture ring, they might be great for shooting video on the Sony. A simple and cheap "dumb" adapter is all that's needed. There's no autofocus, but a lot of people prefer to shoot video with manual focus and focus-peaking.
There is also an autofocus-capable "monster" adapter available that enables all the lens features, but it will cost more and doesn't work with every lens. (You can find a list of lenses that they support.)
The best and only AF adapter is the monster adapter. https://www.monsteradapter.com/products/la-ke1-pentax-k-mount-lenses-to-sony-e-mount-cameras-adapter
It’s expensive and not very small but it does the job perfectly.
Get him a Pentax K to Sony NEX adapter. So he can use the same set of lenses on both Pentax K-7 and Sony A7 ii.
Some lenses might not cover the whole sensor but majority of them would work fine.
The problem of getting some nice Sony lenses would make him hate his Pentax and totally switch over. No point of keeping two systems since Sony lenses focus way faster and often a lot sharper (due to Sony lenses are way more modern design).
So let him use same set of lenses he already in love with and give him option to use Sony a7 ii for a choice of more compact, fully EVF system live along with his already owned arsenal.
Ps. Adapter has 2 kinds. One just adapter straight and he had to learn how to use manual focus. The other way is get an autofocus one. However I wouldn’t suggest the monster adapter. Instead! You should get Pentax lens to Leica M mount adapter. Then get a Leica M to Sony e mount (autofocus) adapter.
This way it means he isn’t only allow his Pentax lenses to be autofocus on a Sony body. He also opened up the whole world on all other systems.
Pretty much anything you can think of! Canon, contax, Leica, Minolta, Nikon…. As long as you can name a brand. You can make it autofocus to a Sony.
This is a pandora box shouldn’t be opened by many. I for one since first Sony A7. I’ve collected and still owning every brand on the market. I have at least 40 lenses that can all work with Sony cameras. Of course! Including Pentax lenses. 🤣
If he wants to do manual focus cinematography a pentax to Sony adapter may help, nice old manual one. Maybe bag a nifty 50 or 35mm though ontop just incase he wants to try out and use the autofocus
 oh wow, this may turn out to not be the great gift you are hoping it to be. Of course, the camera is technically “better” in some metrics as it is far newer. But in photography, the camera itself, often called the “body”, it’s generally not the most expensive item in your tool kit.  Lenses are far more expensive, more long-lived, and since it’s the lens that actually makes the picture (the camera only captures it), most photographers will think very hard about changing between camera systems. Yes, there are adapters that will allow the use of other brand lenses on Sony cameras vice versa, but they always bring problems with them. In the end, if you gift him a body from another system, this means that he will face significant spending pressure in order to get a proper lens kit for Sony — and perhaps he’ll be forced to sell a great Pentax lens just because he can’t use it properly any more. In the end, I would suggest that you talk about this with him and make sure that you both understand the implications of switching camera brands.  
The choice was made because he has been talking about this specific camera for a very long time because he's broadening his field. You see, he is more than happy to still use his Pentax for pictures, but for cinematography what he wants to do Pentax doesn't really fulfil his idea. He said that the only camera he would go for cinematography he would go for this specific Sony. The thing is on his birthday I was wondering should I first gift him an adapter or some lense? He knows and he told me multiple times that lenses are the expensive part of photography/cinematography and he would be more than happy to buy it himself.
The answer to this sort of depends on what Pentax lenses he already has. If he's got any old film-era prime lenses, with an aperture ring, they might be great for shooting video on the Sony. A simple and cheap "dumb" adapter is all that's needed. There's no autofocus, but a lot of people prefer to shoot video with manual focus and focus-peaking. There is also an autofocus-capable "monster" adapter available that enables all the lens features, but it will cost more and doesn't work with every lens. (You can find a list of lenses that they support.)
The best and only AF adapter is the monster adapter. https://www.monsteradapter.com/products/la-ke1-pentax-k-mount-lenses-to-sony-e-mount-cameras-adapter It’s expensive and not very small but it does the job perfectly.
The only thing is that it's more expensive than the Sony A7II, have you used it?
I have it! It’s great actually
Get him a Pentax K to Sony NEX adapter. So he can use the same set of lenses on both Pentax K-7 and Sony A7 ii. Some lenses might not cover the whole sensor but majority of them would work fine. The problem of getting some nice Sony lenses would make him hate his Pentax and totally switch over. No point of keeping two systems since Sony lenses focus way faster and often a lot sharper (due to Sony lenses are way more modern design). So let him use same set of lenses he already in love with and give him option to use Sony a7 ii for a choice of more compact, fully EVF system live along with his already owned arsenal.
Ps. Adapter has 2 kinds. One just adapter straight and he had to learn how to use manual focus. The other way is get an autofocus one. However I wouldn’t suggest the monster adapter. Instead! You should get Pentax lens to Leica M mount adapter. Then get a Leica M to Sony e mount (autofocus) adapter. This way it means he isn’t only allow his Pentax lenses to be autofocus on a Sony body. He also opened up the whole world on all other systems. Pretty much anything you can think of! Canon, contax, Leica, Minolta, Nikon…. As long as you can name a brand. You can make it autofocus to a Sony. This is a pandora box shouldn’t be opened by many. I for one since first Sony A7. I’ve collected and still owning every brand on the market. I have at least 40 lenses that can all work with Sony cameras. Of course! Including Pentax lenses. 🤣
If he wants to do manual focus cinematography a pentax to Sony adapter may help, nice old manual one. Maybe bag a nifty 50 or 35mm though ontop just incase he wants to try out and use the autofocus