These 3 wheel encoders are connected to the TriBot board with 3 thin 3-wire cables. They take 12V as input and output 12V. This means that you should convert the output to 5v before connecting it to the Arduino, which is a hassle.
However, if you disconnect them from the tribot and power them in 5V, they will work fine and output a nice Arduino-friendly 5V.
So the connection of each wheel encoder to an Arduino is pretty straightforward: ground to ground, +5 to Arduino +5 output, and the wheel encoder output to any Arduino pin (preferably one of the interrupt enabled pins), configured as input.
The wheel encoder connector pinout is:
----- | | |...| ------- 123 1: Ground 2: Output 3: +5