1) The scroll lies east of the square where the mission on Earth starts. Get to the demolished road fragment and go all the way down.
Directions: N W N W E
2) You'll find the scroll near the spot where the second piece of the Rod lies. Locate the small side passageway and approach the symbols painted on the wall to unlock the secret automatically.
Directions: N S E W
1) You can find the scroll in the northern part of the Citadel, in the area with the complicated puzzle involving rotating the plates with inactive portals. It takes place during the last stage of Citadel's quest.
Directions: S W E E N