Shard is found inside The Underroot solo dungeon. Entrance to this dungeon is approachable from north, but there are also two ways to reach it from south. Tunnel entrance close to Serpent’s Grotto Wayshrine or tunnel entrance north of Woodheaerth settlement (follow shore) lead both to a Binding Pool. This is the westernmost part of Greenshade. After you reach this point of the map continue north. Another stone entrance leads to the main road that connects this part of the zone with large island to the north. This is the area containing Seaside Sanctuary POI and The Underroot solo dungeon.
You’ll find the shard inside this cave on top of a large rock. This rock is located between the first and the second dungeon floor. As you enter The Underroot keep clearing your way toward the southern part of the dungeon. You are going to end up in a long tunnel. This tunnel leads to the second dungeon floor. Now start clearing your way toward the northern part of cave. As you reach its end you can spot the shine of the collectible in the distance. Exact spot on the second floor from where you should jump onto the rock with the collectible on it is at the entrance of the last cave room. This is the part of the cave where you can find Domina Ssaranth mob that, once killed, marks this dungeon as completed.