This quest is unlocked by completing the quest “In Their Shadow” (https://youtu.be/4LsxcHDtzds) as well as achieving Rank 23.
Shadowbringers Relic Quest Playlist: https://www.youtube.com/playlist?list=PLAIwJ_87EVatVH51HDvwwZOQdUcJxcTNV
source
This quest is unlocked by completing the quest “In Their Shadow” (https://youtu.be/4LsxcHDtzds) as well as achieving Rank 23.
Shadowbringers Relic Quest Playlist: https://www.youtube.com/playlist?list=PLAIwJ_87EVatVH51HDvwwZOQdUcJxcTNV
source