Head west from Aaron to the far west of the city. Head south to where you killed Marin and continue south down the steps. Just to the right (southwest) after the steps is a path leading southwest up a hill to a house. Head along this path and into the house, where you will find Khalim and a couple of guards.
Talk to Khalim, then kill him and the guards to complete the quest.
Jahrin sent you? Haha, many people paid me to incite that dispute. He wasn't as popular as he liked to think. Not because intended to overthrow the Inquisitor - but because he wanted to battle poverty in the port quarters. How appropriate that he is living there now himself. Draw your weapon and die!
Bug? Assassination seems to be a chain quest in that it shows a sub-quest title in the logbook (Moment of Revenge), however, there are no quests that follow it.
Bug: Defeating Khalim and his two guardsmen may not show up in the tasks log for this quest until you have actually completed the task
Note: Although referred to throughout as ‘Goldman’ the NPC’s name tag is actually Khalim. This could imply his full name is Khalim Goldman or Goldman Khalim.