Help with specific simple Schematic design
You could connect Com.A and Com.B to a common ground and then do your switch detection using pullups to the appropriate signals

The datasheet provides all the required information. 
You have 4 wires A, B, Com.A, Com.B (grounds I'd suggest) for the rotary function and the phase relationship of the signals tells you the angular position.
If you are using both Scroll, Jog and Push, then the connections are:



So Com.A and Com.B are your Grounds

Com.A --> A &amp; B your quadrature scroll
Com.A --> S1 is Push
Com.B --> S2, S3, S4, S5 are your Jogs