How do I troubleshoot the touch screen on an HTC Evo Shift?
Try Settings->Developer Options->Show touchscreen touches.  Unfortunately, HTC likes to move these settings around between versions so I don't know if it will work for you.

Replacing the digitizer is possible on many HTCs, I did it on my EVO 3D.  But that's probably what has failed.  Condensation will confuse it and make it stop functioning .