Multiple things. I had it on my front end and the most common things are...
(In order from most common for me atleast)
Balljoints
Tierod ends
draglinks
wheelbearings
Grab your wheel at 12:00 and 6:00, if it has play jerking it back and forth, your balljoints are bad.
If you have had the wobble for a while, it can give a beating to all your DLEs and your TREs
Just check those, by having someone turn the wheel, with and without jackstands supporting the front axle.
Even hold on to it and if you feel a pop or can see visibal wear on the parts, they most likely need to be replaced
Wheel bearings are tested the same way Ball Joints are, except shake the wheel at 3:00 and 9:00 istead of 12 and 6.
If all that checks out you might just have some loose nuts, Check your springs, and the ubolts make sure they are all tight,
even check the bushings on your springs.
-Jon