Strongbox in OOTFollow

Here is a link to the quest.
In Freeport West:
Speak to Nusk Treton on the ground near the Arcane Science building. He will tell you to seek Lenka Stoutheart in Freeport and ask her for the Journal Strongbox, then return it to him. She can be found at an inn in West Freeport, but she will tell you that she dropped the box off a ship straight out from the dock at an Isle in the Ocean of Tears. The strongbox is found in the Ocean of Tears. Get off at the Sisterhood Isle (the first stop), jump into the water and start swimming south-southwest towards the isle with the Oracle of K'Arnon. Look for a shark guarding a bag. Return it for some minor money and xp.
Hope this helps.