You are declarer(West) what you would play at trick one
Contract=6NT
lead = ♣5
Answer is ♣8.
We must play the ♣8 and save the ♣K as an entry. So, we win with the ♣J unblock the ♥K cross to dummy with the ♣K and hopfully run the heart suit for 6 tricks.
Point in blue box to reveal the answer