It depends on what drivetrain you have. If you have 4-wheel drive, then you have two driveshafts (also called propeller shafts), a front and a rear. Each driveshaft will have two U-joints, one at the front yoke and one at the rear yoke, as shown on this part diagram linked below:
https://www.nissanpartsdeal.com/parts-l ... m=370_B001
If you have 2-wheel drive, you'll only have the one driveshaft, but you'll have three U-joints on that shaft, along with a carrier bearing. On some other vehicles, like a '60s Ford Mustang, for example, the driveshaft will only have two U-joints. On yours, there is a U-joint at the front yoke, then there is another one just behind the carrier bearing (part code "37521K" on the part diagram linked below) and the third U-joint at the rear yoke:
https://www.nissanpartsdeal.com/parts-l ... m=370_A001