There may be no 100% line of play, so you should scout for clues. It’s always a good idea in this type of situation to see how much you can discover about the defenders’ distributions.
Say you draw trumps and find out that West began with three and East with one. Before testing the critical club suit, see what you can find out about hearts and diamonds first. If you play three rounds of hearts, let’s say West shows out on the third round. West, therefore, started with a 3–2 pattern in the majors, while East was 1–5.
Try diamonds next by playing the ♦K, ♦A and a third diamond, ruffing in your hand. Let’s say something surprising happens: West shows out of diamonds on the third round. If that’s the case, you know both opponents’ patterns: West started with a 3=2=2=6 distribution, while East was 1=5=6=1.
With this information, you can claim! Cash the ♣K, extracting the only club from East’s hand. Now you can take the club finesse against West in complete confidence to make your contract.
The full deal from this scenario would look like this:
You might wonder what would happen if both opponents had followed to all three rounds of diamonds. You wouldn’t have a complete count, but you would know that West was 3=2=3=5 or 3=2=4=4. Because he holds more clubs than East, he is the player you should play for the ♣Q. The finesse might fail, but you would have given the contract the best chance.