6K Man
Bureaucrat
Sure
In the same line, if an AI conquers a city where you have a national wonder, you can then build it somewhere else.
Followup question: if you build a NW in a city that you later gift to a vassal, say... does the vassal get the NW AND you get to build a new one somewhere else? Or is the first one destroyed? I know that other improvements survive when a city is gifted...