I've done plenty of searching.

I looked under my car and noticed my aft O2 sensor wire cut and hanging. Where is that cable routed to? Is there a wiring diagram so I can re-wire?

 

There should be a clip under the car about a foot/Foot and a half from the O2 sensor location. If the clip is gone and the wire is cut before the clip you will need to replace the clip by soldering on a new wire with the clip. That's what I would do at least. Instead of buying the O2 sensor then cutting it. But it's up to you.
Do not just use connectors cause the impedance will be different and may cause issues.