After accepting the contract, if you look at the map, you will notice that there is a brand new circular restricted area over to the northwest with a red skull indicating the assassination target. This is in a raised rocky area overlooking part of the town below. Once you begin the contract, head over to the target location.
Approach the restricted zone from the street running past it on the west. From here you can scramble up a few rocky ledges and enter the guard post. Hide behind the crates at the top of your passage up and peek out from behind the corner. Whistle and perform a corner takedown on the closest guard. Next, move into the stalking zone and repeat with the other guards in the area.
From here, you should be able to spot a dirt path leading south, slightly uphill to your right. Activate Eagle Vision whilst looking up the path and you should identify your target. When you deem it safe to do so, sprint up the dirt slope and assassinate him to finalise the contract.