The flight AF447 needed a 3 pilots crew.... at T/O ! With adequate and valid licenses, qualifications, autorisations, recorded in the Air France files. The captain has to verify that before the flight, not in flight before the rest of the captain. Or did M.Dubois say that as a joke ??
I don't think it was a joke.
The license requirements to act as second in command are not the same to act as PIC (i.e., during the captain's absence). Seems to me he was asking if he was qualified to act as PIC, for it was right after that that he said that FO Robert would be taking his place in the left seat. (and due to AF policy/practice the cruise pilot in the right seat was PF and PIC).