This is the scenario and it’s slightly geeky:
You are involved in a transporter accident similar to that which always seems to be occuring on Star Trek (why not just take the shuttle?) and an exact duplicate of you is produced. Instead of one of you being “Evil Kirk” both are exactly the same. This was also the sort of thing that The Prestige glossed over….
A transporter functions (for the sake of argument) by making a copy of your atoms in a remote location and then destroying the original atoms. OK not destroying but converting them to energy. This means that technically both versions of you are duplicates and the original no longer exists. At least not in a form that could be considered you.
Which one is you? If one duplicate dies is the other one you?