Washed To Strange Shores With The Fleet Skyshard

Guide:

Northeastern Coldharbour, south of the nearby The Wailing Maw solo dungeon, east part of The Lost Fleet (Lighthouse POI). East of Reaver Citadel Wayshrine.

Skyshard is on the water, next to corals. This part of the map is called Coral Tower. You need to be on a certain quest that lets you climb the Coral Tower through Coral Tower Tunnel.
This quest is called “Between Blood and Bone“. You can accept this quest upon successful completion of “A Graveyard of Ships” quest. Get Graveyard of Ships from Captain One-Eye. You can find Captain One-Eye in a small camp, next to the road that leads to center of The Lost Fleet (Lighthouse POI).

Note: In order to reach northern part of Coldharbour you need to complete the main quest “The Army of Meridia”.

Update 1: Just west of solo dungeon Wailing Maw map mark there is a large wooden pole. You can use it to climb toward the platform with the shard on. Keep on mind that you have to make one final jump from the pole’s top in order to reach the platform.