http://www.ti.com/lit/ds/symlink/cd74hc75.pdf

In a latch iC like the one linked above. It has the Q and (Q with a line above it) outputs.
In these outputs if "Q" is "on" sourcing current, is the other "Q" sinking current? or is it just off?

 

Yes, sinking/sourcing current is one way of looking at it.

!Q is just that, opposite of Q.

If Q is high, !Q is low
If Q is low, !Q is high

Flip flops have the complimentary output, as sometimes using both is useful