It could be a lot of different things, but you need to start by getting underneath it and looking for worn parts. Get a helper, if you can, to be at the steering wheel, and move it back and forth as you watch and feel for lost motion at steering joints, tie rod ends, pitman shaft of steering gear, etc. Make sure there is no play at the ends of the track bar, especially at the ball joint where the track bar attaches to the frame.
Wobble will be worse if your steering damper is worn out, though in theory at least a perfectly set up front end should not need a damper at all. Check the damper.
Check your ball joints. Jack up one side at a time, by the axle tube, and first try pulling and pushing at the top of the wheel. There should be no play. then get a lever and try lifting the wheel up. Look for visible up-down movement at the ball joints. There should be none. Bad ball joints will contribute to wobble, and tend to make your tires wear on the inside.
Finally, check your wheel balance. Actually you should probably check that first. You'll wobble if your wheels are out of balance, no matter how good the rest of your vehicle is. Especially if you have alloy wheels, you need to check balance occasionally, because the weights can fall off. In addition, if you do have worn steering parts or bad alignment that is causing uneven tire wear, the wobble will get worse due to the tire wear.
