How do I edit the rendering code?

I want to check out the rendering code for BeamNG, what file contains it?

 

BeamNG is not open source, although it's graphics engine, Torque3D is. You should be able to find the source code for that on Torque3D's website.

 

You cant.

The renderer is in C++. Compiled code, not editable without the full source code and a C++ compiler.
You can get the T3D render code, except thats DX9, BeamNG rewrote a DX11 one. You cant get the C++ source for BeamNG