Location: This quest can be found in Nautica.
Objective: Find the Human Singer the Mermaid Used to Listen to
After talking with the mermaid, zoom (fast travel) to Gondolia and head to the grand stage. Facing the stage, turn left (east) and follow the path to the eastern lighthouse. You will find an old sailor with a beard and a blue cloak there. Talk to him and tell him about the music-loving mermaid. Agree to learn the song and head back to Nautica. Make your way back to the mermaid near the palace and talk with her. The quest will complete as soon as you are done serenading her.
Reward: Gracos’s Trident