Does my 05 G35 6MT "RevUp" have a factory wideband o2?
If so how do I wire up an A/F gauge to it?

 

Yes
You can log your A/F a data-logging software such as Cipher.
If you're looking to put a gauge in the car, there might be install info in one of the DIY's or the FI section. I'm guessing the gauge would be wired into the ECU somehow.