Here are locations to the 12 gestures (gesture name / NPC / location), if "Learn Gesture" isn't available from the character, just keep talking to them to get the gesture.
Welcome -- Saulden the Crestfallen Warrior -- Majula
Duel Bow -- Blue Sentinel Targray -- Cathedral of Blue (A Token of Fidelity is required in order to speak to him, also you need to join his covenant before you can learn the gesture)
Mock -- Straid of Olaphis -- The Lost Bastille (A Fragrant Branch of Yore is required to unpetrify him)
Fist Pump -- Creighton the Wanderer -- Hunstman Copse (In a locked room, key is found in another cell nearby that you enter via the ceiling)
Praise the Sun! -- Heirs of the Sun Altar -- Harvest Valley (Joining the covenant is needed to learn this gesture)
Prostration -- Laddersmith Gilligan -- Earthen Peak / Majula (You need to pay him 2000 souls if you want to learn it at Earthen Peak, otherwise if you exhaust all his dialogue, you can learn it for free at Majula)
Joy -- Benhart of Jugo -- Majula (Only available after unpetrifying Rosabeth of Melfia)
Decapitate -- Head of Vengarl -- Shaded Woods
Warmup -- Manscorpion Tark (After defeating Scorpioness Najka, speak to him with the Ring of Whispers equipped)
This One's On Me -- Chancellor Wellager -- Drangleic Castle
Have Mercy! -- Grave Warden Agdayne -- Undead Crypt (If you are carrying a torch, he will be hostile towards you)
Hurrah! -- Captain Drummond -- Memory of Vammar