Back in 2014 it would seem this quest chain was problematic, where players were unable to complete the objective to defeat the servant of Naemon. I just discovered this same bugged quest on PS4, and tried abandoning the quest and restarting it. Soon as I abandoned it I began to search the same area for Indaenir, the lil' Bosmer dude that was accompanying you on the quest. Sure enough I found him and started the mission he was providing, which was actually a version 2 of the same mission. It featured a different objective in the same area which resulted in the same objective to defeat the servant of Naemon, and in this version of the mission I was able to spot the servant and defeat him. It seems if people are naturally starting the quest chain on PS4 (not sure about other platforms), via the Queen's assignment in the nearby town of Marbruk, they are being forced into version 1 of the mission, which is still glitched.

I'm assuming at some point the mission was redone, because the 2014 issue was apparently patched, but I don't have details on what was done to the mission. In any case, this could use some looking at to make sure Aldmeri Dominion player quest strings are taking them to the correct mission variant. Progression halting bugs are the worst.