the hub is the part where the studs are attached to.

the hub is then pressed into the knuckle which is the big piece of metal that the brakes bolt too and that the ball joins and tie rods attach too. You are going to have to rotate it till the broke stud is lined up with the notch on the backing plate. Then you are gonna have to knock it out with a sledge hammer or an air hammer.

if it doesnt come out that way, and by looking at how that one is designed, you are going to have to unbolt the whole spindle from the strut, lower control arm, brakes and tie rod. Yours looks like a press in style, so you are gonna have to get big hammer or air hammer again and knock the hub loose from the bearings in the center. then knock the stud out and install a new stud, then put it all back together.