Is it Camp Nou or Nou Camp?

It is Camp Nou, but the truth is that both are correct. It took a referendum of the club members who, in 2001, voted to make "Camp Nou" the official name of the FC Barcelona stadium.
The explanation is that in Catalan the adjective "new" (nou) can be placed before or after the name, in this case, "ground" or "field" (camp). Camp Nou" and "Nou Camp" were, therefore, both technically correct until "Camp Nou" was recognized as the only correct form in 2001.