Where do I attach the rails for the keyboard tray on this desk?
Assemble the rest of the desk, it should become self explanatory with what holes are left. This is probably contrary to the instructions, but you will be able to reach inside to attach the drawer slides later.

Picture 1 is the right side face of the middle upright

Picture 2 is the inside face of the left upright.

Picture 3 is the inside face of the right upright.

The feet go on the sides opposite the embedded metal lock nuts.