What level of graphics programming and/or reverse engineering expertise do you need in order to dissect a frame like this? I wouldn't even know where to begin, but I'd love to be able to do stuff like this!
If you specifically want to do something like this you can use RenderDoc (https://renderdoc.org/) and simply run a game through it. You should get a result that's pretty similar. The deferred shading technique used in GTA V is now pretty much the standard way of doing things in most AAA engines I know of and is pretty well documented. Mozilla has a great article about using it in WebGL : https://hacks.mozilla.org/2014/01/webgl-deferred-shading/
