Tail and brake lights on right rear are out

On a Jeep Grand Cherokee, the most common problem are the light sockets the bulb goes in. The sockets have little contacts on the edges that become worn and don't allow the bulb to light up. The sockets usually have to be replaced and can be bought at ant parts supplier.

The most common culprit is a blown fuse.

Your manual should be able to direct you to the location of the fuse box and applicable fuse. Replace fuses only with those of the same rating called for in the manual.