If you are referring to the tab on the axle, in your picture, that is a little rusty and has nothing attached to it; that's where the original position for the swaybar link was attached. the bracket it is attached to now apparently came with the lift.
Wait a minute, I just looked at your picture again. It looks like the plate has spun out of place. I see what you mean now. Look at the bolt on the other side of the Jeep and get a grade 8 bolt from the hardware store to match it's size and length. It must've vibrated loose. Might want to torque all you bolts while you're at it.
2010 Rubicon, 4" lift, Currie control arms and trackbar, 37x12.5x17 Goodyear MT/R kevlar