* Driveshaft(s): There will be at least two U-joints. One is located at each end of the driveshaft connecting the transfer case to the front axle (if engaged). There's also a driveshaft connecting the transfer case to the rear axle, with U-joints at both ends of it.
* Front Axle: The front axle itself may have U-joints in the axle shafts, depending on whether it's a Dana 30 or other type of axle. These are inside the axle housing and not readily visible without disassembly.
* Rear Axle: Similar to the front, the rear axle (typically a Dana 35 in a 97 Wrangler) will also likely have U-joints within the axle shafts. Again, these are internal.
In short: You'll easily see the U-joints on the ends of the driveshafts. The ones in the axles are internal and require disassembly to access.
