Extinguished Eye

Zone: Suramar
Vendor: First Arcanist Thalyssra - /way #680 37.0 46.2 First Arcanist Thalyssra
Faction: The Nightfallen - Revered
Cost: 500 Gold

You will need to progress through Suramar's campaign quest chains to unlock Thalyssra. To begin this chain, visit Khadgar in the Violet Citadel and pick up the quest called Magic Message.

If he doesn't have this quest for you, it may be due to you not being a high enough level. Suramar was a zone for Legion max-level characters to unlock, so you may need to be whatever the 'max' is for Legion content. Given that we experience level squishes every so often, this number will change over the years.