This page shows the location of the shanty called "Drunken Sailor"
You can find it on a house in center Nassau:
Here is the map:
How to get[edit]
Climb to the roof of the house
Chase it and you should catch it above one of the roofs it floats to:
Otherwise if you did not catch it just leave area (best is to fast travel to the viewpoint in the east) and the song sheet should respawn in the original location