Snuffing Them Out is a side quest in Tyranny.
The surviving Sages are an annoyance to the Scarlet Chorus at the Burning Library, and the Censor would like you to deal with this annoyance.
Note that you can choose not to complete this quest; after Betray Alliance (while avoiding Effigy before that), you can then do Language of the Ancients instead.
Contested Lands: Extinguishing the Flames
Lethian's Crossing': Blades of Iron → Iron and Blood → The Bronze Thief → Forbidden Passage
Stone Sea: The Tiers Will Shake → Carving the Path → Securing The Sea
Lethian's Crossing': The Symphony of the Forge → Blood and Bronze → On the Hunt → Finding a Madman
Contested Lands: The Silence of Secrets
Stone Sea: Cairn's Final Song → Fangs and Fury → In Pursuit of Cairn
Blade Grave: Battered but Unbroken → A Daunting Path → That Which Remains → A Breach Between Worlds → Making a Stand
Stone Sea (Stonestalkers): Unlikely Allies → Purge the Stone Sea → Followers of Cairn
Stone Sea (Earthshakers): Unlikely Allies → Forging the Way → The Rise of the Earthshakers → Fortifying the Sea → Arcane Preservation
Contested Lands: Heated Words
Lethian's Crossing': The Forge Master's Prize → Assault on the Crossing → Artifact Hunter → Finders Keepers
Blade Grave: Undaunted → Relic Hunter → Bound by the Blade
Stone Sea: Blood Trophy → At Any Cost