If you haven't done so already, read the "Chassis Lubrication" article as there is some relationship between between the two subjects. Jaguar thoughtfully provided lube fittings for the wheel bearings but the wheels must be removed to find them. The service manual recommends a 15,000 mile (25,000 km) interval for this service. My suggestion is to do this every 6,000 miles (10,000 km) when you rotate the tires - it's an ideal time, convenience wise.
Rear bearings are all too often neglected on Jaguars. On the rear hub carriers (large aluminum casting just behind the rear wheels) you'll see two small caps about 5/8" in diameter. Clean the area thoroughly and prise ("pry" to the yanks out there) the caps off. Now exposed is the rather large cavity which contains the bearings. There is no grease fitting. Insert the nipple of your grease gun and pump in grease until the cavity is full, rotating the axle a few times to help distribute the grease. Reinstall the cap and you're done.
If you followed the advice in the Chassis Lubrication section you'll already have your grease gun loaded with proper bearing grease, not simple "chassis lube".
The front hubs also have lube fittings for the bearings. These need to be lubed until grease comes out of the bleed hole in the center cap. After you've lubed the bearings check for bearing play by grasping the wheel at the 12 and 6 o'clock positions and gently rocking. The specified play is .006", barely discernable. If you feel more than this - just about any amount will be more than .006" - the bearings need to be snugged up. That's another topic, though.
Although not mentioned in the Jaguar literature, the front bearings should be cleaned and repacked with fresh gease from time-to-time. Some qualified sources say that if you really do a good job, clean the bearings and hubs perfectly, and use new seals and premium grease, then every 50,000 miles (80,000 km) should do the trick. Assuming regular re-greasings in between, of course. I prefer a much shorter interval, every 25,000 miles (40,000 km). If you've just bought your Jag and don't know if this has ever been done it would be a good idea to go ahead with the job regardless.
Be advised, though, that a complete front bearing repack on a Jag is a bit tricky, much more so than on some "ordinary" cars. You have safety wire, caliper alignment shims, and difficult-to-reattach steering arms to contend with. Before doing this, even if you've done it on other cars, do some reading up on the subject so when all the shims start falling out you won't be surprised!
Anytime you lube the bearings give the wheels some spins and listen for the "dry" sound of a faulty bearing. A worn bearing will never mend itself and must be replaced. With regimented lubrication the bearings will last 100,000 miles (160,000 km) easily, sometimes much longer. Of course if they've been allowed to go dry, they'll be ruined much, much sooner.