As South, you barrel into game and receive the club queen lead. You play low from dummy and ruff the club continuation. What now?
You have plenty of chances in the red suits, but the trick is to combine them. When you lead a spade to the king, East wins with the ace and plays the club ace. You ruff high, preserving your low trumps as potential entries to dummy, and then cash your top hearts. If an honor falls, you can reenter dummy in trumps and then run the heart 10 to set up your game-going trick. Alas, everyone follows low to the hearts, so you will need to tackle the diamonds for one loser now and will naturally start the suit from dummy.
You plan to cross to North in trumps to broach diamonds, but the question is which finesse to take. Dummy’s powerful diamond spots offer you an alternative to a simple finesse of the jack here. As is often the case when you are missing two honors and a spot card, your best shot is to take a deep finesse at some point, playing East for the diamond nine and one of the missing honors. This is better than leading to the jack initially, which only allows for the one case of a K-Q holding versus the two possibilities of K-9 or Q-9 with East.
You could run the diamond seven at your first chance, intending to reenter dummy in trumps to finesse the jack, but it is better still to start with the diamond 10. This also picks up honor-nine doubleton with West. Either play works here — only finessing the jack on the first round fails.