How to get the clapping gesture

bloodborne

How do you get a clapping gesture? I have seen other hunters clapping and I'd like to know how to get the gesture myself.

I believe you are referring to the "Approval" gesture. You can get this gesture by following Eileen The Crow's questline.

To start the questline you must meet Eileen in Central Yharnam, she can be accessed through the sewers and the room she is hidden in is hidden behind breakable objects. By speaking to her you will have also started the questline.
Her next location is in the Cathedral Ward, she is waiting just to the left of the front exit from the lamp. When speaking to her she will alert the player that she is hunting a hunter at the Tomb of Odeon.
At this point the lamp at the Tomb of Odeon would be disabled, and the player must backtrack from the Cathedral Ward to the tomb. Eileen's quarry will be waiting, and he will attack you. At this point Eileen will aid you to kill the hunter. As a reward for helping her kill the hunter you will get the Approval gesture. Note that she can be killed in the encounter, and hitting her may trigger her to be hostile towards you.