newby needs help with P0420

guys new here, just picked up a 2001 cherokee with 148K for a daily driver. runs great but throws DTC P0420, catalyst efficiency. I know it needs a new cat, but where in the hell is the rear o2 sensor measuring this efficiency?

i see the qty 2 upstream o2s in the manifolds, but where is the rear o2? i cant find it for the life of me, it is no where near the cat or ,muffler.......

thanks again guys

by the way the jeep runs great, idles smooth, and does not have noxious exhaust, but still going to put a new cat in there, just needing to know where the downstream o2 is

I just sent to your yahoo email account, a PDF picture of where the 02 sensors are located on an 01XJ. (can't figure out how to post it here).

thanks! yes i received it....i was thinking i only had that one big cat, didnt know about the ones on the manifolds, thank you!