How do I load an .obj file into opengl in objective c /cocoa?
This has a lot of information about the OBJ file type: http://astronomy.swin.edu.au/~pbourke/geomformats/obj/
It’s just an ASCII file, so all you have to do is parse it and send the appropriate OpenGL commands. You would have better luck looking for some C code on how to do this then just add that to your Cocoa project.
Another good source of information (as always) for file formats is wotsit.org. They also have the source code available to do it.