Every jeep/tire combo is different, you can do the chalk test or experiment. When I went to 35s on my Rubi I tried 18 to 28 psi.
I like 20 for the ride and wear. I've went up to 24-26 to see if fuel mileage picked up, couldn't tell much if any difference, gets around 15 on the highway. I use 8 psi on the trail and redrocks.