As a simple rule to get pinouts. Stereo pots will have 2 lines of 3 pins, each line represents one channel.
Turn the pot to minimum and measure the resistance between the pins, and then to maximum and measure the resistance.
Wiper: Will be the pin where at minimum and maximum the value changes. I.e. the other 2 pins will stay at 10, 20, 50 or 100k regardless of pot position.
Input: When the volume is at minimum the resistance between input and wiper should be high, when volume is at max resistance between input and wiper should be low.
GND: When volume is at min, res between GND and wiper should be low. When volume is at max, res between GND and wiper should be high.