My partner opened a "strong" one NT. I am holding:
What should I bid?
I would bid 4C (Gerber) to ask about aces. If partner has 3, bid 7D. If partner has only 2, bid 6D.
The weak point in this hand is if partner has, say, the KJ in spades; some other responder might have a fancier convention to pick out the specific high cards.
You have to make a forcing bid, what you specifically bid will depend entirely on what conventions you and your partner are playing with.
Now that this is open again:
Opposite a strong 1 NT, I bid 3D if it is natural, or I transfer to diamonds if that is available. If partner denies support for diamonds I bid 6D. If he shows support for diamonds I investigate 7D with what-ever methods are available to me. Consider where partner's 16 points are. An "unfortunate" hand from partner would be this: AKJx AQx xx Qxxx, and 6D is looking pretty icy even with all those wasted values in spades. In a practiced partnership I investigate grand slam even if partner denies diamond support initially.
Opposite a weak NT I will probably still end up in 6D, though I might blind the auction by jumping there in an unpracticed partnership. Why help the defence by bidding precisely when it is going to be of more help to the defence?