What should South bid, after partner opens with 3Nt?
AgAin, don’t forget that the 3nT opening shows a long solid minor and nothing outside.
You must therefore, between you, be missing two aces, so no question of a slam arises. nor have you a suit of your own which could possibly be better than clubs — which you know, by definition, must be his suit.
You could bid 4nT, which asks opener to convert to his minor suit at the five-level, but yours is not a hand on which it will be an advantage for the lead to go up to north’s hand, and nor will it matter at all if your hand is dummy. Bid 5♣, which shows a hand on which you wish to be in game.
Some theorists, incidentally, play 4nT as a slam try, suggesting that opener should press on to six in his suit holding an extra trick, but this would avail nothing here, as he definitely shouldn’t have either the ♠A or ♦A.