It's impossible to do that on SE sites - if you try to flag as a duplicate, the site requires you to chose the question you believe the one you are flagging to

It's impossible to do that on SE sites - if you try to flag as a duplicate, the site requires you to chose the question you believe the one you are flagging to be a duplicate of. The ability to vote is disabled until you do, and the site then shows the link in a comment and eventually at the top of the post if it gets closed.