It's going to be different depending on the brand of tire you run. Different brands have different sidewall strength, which will give a varying contact patch on the road at a certain air pressure. You will need to run less air with a stiffer sidewall, and more air with a softer sidewall, to get even tire wear. It also depends a LOT on rim width. Narrower rims need less air to get an even wear pattern, wider rims need more air to keep from wearing the outsides of the tires.
I run 40 lbs. in my Swamper TSL Radials, merely to make them run on the center of the tread onroad so as not to wear the outside lugs. It also makes the tires slip easier in turns, since I run a rear Lincoln Locker
Try running a chalk line across the tire tread and run a short distance to see if the tread is wearing evenly. Adjust pressure as needed.
I'd start somewhere between 30 and 35psi on the road...and adjust from there. Offroad, It all really depends on a lot of things--mostly if you have a way to air back up or not incase you break a bead from being aired down too low.
I'll also say that onroad pressure also has a lot to do with the type of vehicle (heavier vehicles would need more air pressure than a smaller one) and the type of tire.