this doesn't have to do with this (well it sort of does) im doing that mission and there is a puzzle near the end which is impossible and i've searched everywhere and there is no clues (don't troll plz)
If you're at the six pillars (three on the left, three on the right and a gate directly in front), look up and behind the pillars for your clues.
Edit: to the OP, I don't know. I had picked up the quest you're doing, but had joined the College before following up on the second and third pieces.