Most players will probably have an understanding that
King asks for Count
Ace asks for Attitude
Many will also have an understanding that Queen also asks for Attitude.
Against NT contracts it is usual to agree that King leads also ask for an UNBLOCK of an honour, failing which you give Count. This is critical in helping partner to decide whether to continue the suit.
(a) Play ♠ J (the unblock). Partner holding AKQ109 will now know what to do.
If you played ♠ 7 partner may think declarer has ♠ Jxxx and switch.
(b) Play ♥ Q (the unblock). Partner holding AKJ10 will now know what to do.
(c) Play ♦ A and return the suit. Happy days!
(d) Play ♣ 7 (count denying an honour). Please don’t play ♣ 3 because partner probably won’t know whether you’ve got an even or odd number of cards.
GIVE CLEAR COUNT WHENEVER POSSIBLE.