I'm not sure if I get you. But if the "body" and "hand" are separate objects and the hand is pinned to the body, you can use
"Pick by comparison" like this
Pick "hand" which body.UID = hand.pin.pinnedUID
It means even if there are more than 1 hand object instance in the layout, you're picking the hand that's specifically pinned to the body. Just add another condition if there are multiple body instances in the layout select which (or "for each" condition) instance of body object.