By ground I assume you mean common for the analogue in?
If you apply power and measure the voltage across the pot, it should typically be 0-5v/10v.
The '0v' end is the common.
Shouldn't take much to reverse engineer the whole board, the IC, according to the print pattern is most likely a 555?
The POT does not appear to be at P.S. common, but the 0v end will still be the common for signal purposes.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.