The wheels for the prototype jeeps, and early production 1941 to early 1942 jeeps were a one piece construction, and these are hard to find because few were made, and they were replaced by later wheels.
The ones used in jeep production from early 42 to end of production in 45, and on the jeep trailers, were a two piece construction, which allows the wheels to separated into two parts to take the tyres off without special tools in the field. These are more common than early one piece, but still rare because they were relatively fragile. This meant they often don't survive well, and that they were replaced with a different type of one piece wheel on civilian and miltary jeeps after 45.
Two piece 'Combat Rims' are the easiest to spot, the one piece is harder because there are many similar post war ones.
After that brief introduction, here is a site telling you almost everything you need to know. If you still have doubts after that, send pictures to Godevil or myself, we'll be glad to help.