During the Prologue - Barricade mission where you have to destroy a gate by using a ballista, drop down the wall to a series of scaffold and down to the ground. You will have to fight several soldiers from the rebellion group and make way to the guarded ballista. After finishing off your enemies and cleared the square, head back further back from the ballista and look to your right beside a house and you will see a dead man dressed in a white robe with a red belt (Altair Ibnu La Ahad reference) laying face down on top of a broken hay wagon. Looking a up and there's a wooden ledge with some bird sitting around where assassin usually survey the surrounding (synchronize) and perform the leap of faith. Geralt will give a funny monologue that he commonly used in a fight that sounds