Likely the trac bar top joint or ball joints. Though most any loose steering rod joint can pop when it shifts suddenly.
Ball joint noise seems to happen for me when I turn into a driveway, a bump during a turn and a pop, is when I first notice.
Trac bar I often notice on any old bump and usually the steering wheel center point shifts. Steering wanders on a straight road.
Control arms can jolt a little when starting or stopping (usually doesn't make any/much noise), most noticeable when starting stopping at slow speeds or when parallel parking.
Steering rod pop, is often noticeable when turning the wheel and changing the direction of turn, at stop or at very low speeds. May also add to wander when driving on a straight road.
The way I test my ball joints is to support the axle, wheels off the ground on jack stands. And lift under the tire with a 3-4 foot piece of 2X4. If you have somebody else lift and have a flashlight handy you can see the ball joint movement, most any movement is too much.
At he same time grab the tire top and bottom and push/pull reversing the sequence a few times, to check for hub bearing play.
While you have it up there jam something into the axle yoke (as a stop), turn the tire until the axle jams and look at the U joint, check for movement at the rubber seal on the cap bottom.
As a matter of fact a good time to check the whole front steering system.
Get to know your XJ intimately, crawl up under her skirts and inspect her under body.
