Joystick to Computer Wire

Is there some kind of wire that can connect a joystick to a computer (while a joystick is connected to the robot via VEX net) ?

Yes, but you need the RobotC wireless downloading cable:

If you’re using easyC, there is no way to do this, sadly (one of the reasons we now use RobotC).

You can wireless upload with EasyC (at least V4 can) , but we have had trouble with wireless code uploads and RobotC. We use A-A to upload code, and will use the programming cable for debugging.

You need the Programming Hardware Kit.

RobotC, EasyC, PROS, Robot Mesh, and Simulink all support wireless programming with this kit. With that said, it will obviously not perform as well as a direct USB connection, and the different programming options will exhibit different extents of performance degradation (different frequency and quantity of data transferred).