So it says explore traitors passage, went through the whole map a few times, kill the assassin boss etc. But i dont seem to get an update on the quest.

I have this issue also, would be interesting to see of anyone has any insight on this.

Isnt this in the Trial of Sekhmas that you need to complete in order to get your first ascendency?

Killing the assassin isn't part of that quest. I assume your on the quest that says "search the traitors passage" or however its worded. That quest won't update until you get into the next area. Killing the assassin is just a side thing.