Guide:
Northeastern Reaper’s March, just north of Fort Sphinxmoth Wayshrine.
There are two shards at this location. This one is not inside the solo dungeon. You can find it standing next to a small stone wall next to the path that leads to Fort Sphinxmoth.
Close to Fort Sphinxmoth Wayshrine you can find Rafora Casca. Rafora gives the quest “An Affront to Mara” – part of Fort Sphinxmoth Objective. This quest takes you to Marcella Ammianus and entrance to Fort Sphixmoth. They are both close to this collectible.
