It exactly sure what this thing is mounted behind my front bumper on the passenger side my question is what is it and where can I relocate it

 

That's your vacuum reservoir. Some say they put it under the battery tray. I've got mine where the air box was. The K&N filter shroud left enough room underneath.

 

The vacuum reservoir holds a vacuum to run your cruise control (if you have it) and operate your ventilation system. You can relocate it anywhere you can run a vacuum line. Just find a spot under the hood where it will fit and not interfere with anything. A lot of people put it up near the firewall.

You can do a Google image search for "jeep xj vacuum reservoir relocation" (or just click that link) to get some ideas.

 

I found a bolt hole above the frame and used a wire tie on mine 4 yrs. ago thinking I would remount it later, well...........