West leads the K against 3NT. South can count 1 heart winner, 5 diamond winners, and 2 spade winners. The 9th trick must come from either spades or clubs.
While it may seem plausible to lead clubs twice to establish a club winner, it's better to simply play West for the Q. Based on the auction, West should have six spades, leaving East with a singleton. Accordingly, South can cash the K (in case East pops up with the singleton queen) and lead a spade toward dummy for the "marked" finesse of West's queen.
The full deal:
North
AT5
8542
West
KJ3
East
Q98764
JT5
2
KQJ
9763
5
South
9876
932
KJ3
AK84
AT
AQT42
Q76
Had South mistakenly led a club instead, the contract would go down. East would win the K, put West in with two hearts, and then regain the lead with the A. The 9 would be the setting trick.
See also
Backward Finesse
A finesse that's taken in the "opposite" direction of a regular finesse.
Chinese Finesse
The lead of an unsupported honor as a pretense to a legitimate finesse.