Warning The Exarch usually stands just in front of the book so make sure that everyone gets the update from the book before you kill Trulnariz!
You now need to find four keys from the Scaleborn harbingers that spawn in the same room. This is an uncommon quest update.
They are also in a few other locations if it's crowded. Try the Banisher Prepatory ( 170, 60, -50 ) /waypoint 170, 60, -50 (as you leave the exarch room hang a right).
Go back to unlock the book The Chant of the Exarchs.
You must now collect 8 pieces of paper and 8 pieces of chalk.
Slay 8 Droags (any type) to get 8 wings like paper.
Find a droag who can help you translate the map. Take the map to a Scaleborn blasphemer ( 78, 126, 171 ) /waypoint 77.91, 126.14, 170.87 in the Scaleborn Cell. (If youre unable to target him, just scroll into 1st person and stand really close to the cell, this should do)
Take a sacrificial blade from the Ceremony Weapon Rack in the Room of Recovery at ( -173, 43, -180 ) /waypoint -173, 43, -180.