Note that Page 2 is in the same side-room as Tserrina's Diary was found in. Pages 1 and 3 are in other side rooms, which do not become accessible until after Spectral Librarian Emiida is defeated. Pages 4 and 6 are downstairs in the library itself, whereas Page 5 is upstairs.
Add the pages to the diary (examine the diary in your inventory).
Place the diary back on a table where you originally found it, at ( 115, 45, 53 ) /waypoint 115, 45, 53.
Simply picking up this quest (by clicking on the glowing book) can update the quest The Tower of Frozen Shadow for the relevant step. For this to work, you must not already have the quest "Tserrina's Strife" in your journal, this quest must not already have been completed by anyone in this zone instance, and of course you must be on this step of the The Tower of Frozen Shadow quest. Note that the update is not obtained if you accept the quest being shared to you.
This quest is repeatable (although it is not marked in the journal as such), but will only give XP (and AA XP) once.