We really don't know exactly where Pan Amsterdam comes from. He was found on the coast of Miami Florida in a state of apparent amnesia.
Nonetheless, Pan Am is clearly from the U.S.A because he has a North Eastern American accent. Although we haven't been able to pinpoint it, the accent sounds like a cross between Brooklyn, Manhattan, or Jersey.
As for why Pan Am was found at sea we don't fully know and are still investigating. We are presently investigating a story where a Jazz trumpet player was lost at sea and jumped ship from a Neo-soul, Smooth Jazz cruise...