If player 1 got enough resources for noble A and B, because the game only lets players obtain 1 noble per turn, player 1 got noble A. Then player 2 got enough resources for noble B. Who will get noble B, is it player 1 because it is a "noble in waiting" or player 2 because of turn player priority.
From the rules:
At the end of their turn, each player checks the noble tiles in order to determine if they’re receiving a visit from one of them. A player can be visited if they have (at least) the quantity and type of bonuses indicated on the noble tile. It is impossible to refuse the visit from a noble, which is not considered to be an action. If a player has enough bonuses to be visited by more than one noble at the end of their turn, that player chooses the noble to be received.
So player 2 will receive the noble in this case. It does not matter whether player 1 also has the requirement; you only receive a noble when it is your turn.
Note that if it were the other way, and noble B also were "in waiting" for player 1, then there wouldn't be much point to limiting it to 1 noble per turn. It would only make a difference in the rare case that the second noble would cause the game to end. The point of limiting the nobles to one per turn is to give the other player(s) the chance to get the other noble for themselves.