I was checking out underside of my jk and everything was protected by skid plates but this one plastic box. Does anybody know what it is? and what I can do to move it or protect it?

 

If its towards the rear of the vehicle, it is the evap canister. You can either move with the woods relocation kit or get a skid plate for it.

 

Sounds like the evap. canister to me too. I'd advise relocating it. Kilby and Woods make relocation kits. They differ in their approach though. The Kilby puts the canister between the underbody and a steel plate. The Woods kit modifies the stock mount and requires you to drill holes in the body. It mounts to the plate on the body instead of using the metal plate underneath. You could argue that you really don't need it. I chose the Kilby kit because you don't have to drill into the body.

 

If you go off road, it would be a very wise decision to get the relocation kit. I didnt know until it was too late.