Back to Skellige
To the north of the Giant’s Toes Signpost you’ll find a few small islands just off the coast. One of them has this quest that will pop up if you get close enough. If you leave without completing it the quest will disappear.
Swim over to the island to find a few bandits looting the crates from a shipwreck. Kill the Bandits and examine the crates. One of them has the sword, Solid Skellige Sword, and another has Clan Brokvar’s Insignia on it.
Make your way to Spikeroog to the village of Svorlag and speak to the Merchant by the docks. He tells you the ship must have been one of theirs that sailed out a month ago. If you found the sword you’ll hand it over for a reward of 55 Crowns. If you didn’t find the sword you’ll still be paid a reward of 50 Crowns.