The Masterson Amulet - NWN Side Quest (Chapter 1)
Docks: The Masterson Amulet is a side quest that begins by speaking with Hemmel Masterson in the central portion of the Docks District. You'll find Hemmel standing next to a group of trees near the merchant stalls in the south, use my screenshot above if you need to see the exact location.
For this quest Hemmel asks you to retrieve the Masterson Family Amulet from a man named Callik who is found in the Sewers portion of the Docks District. During the main story quests involving the Docks District you'll actually encounter and have to kill Callik, you'll likely find the Amulet at this time.
I recommend you check out the Docks: Trouble in the District quest walkthrough for more information about how to reach Callik and beat him.
If you missed the Amulet the easiest way to get back to where Callik was is to travel through the sewer grate northwest of The Seedy Tavern. This will put you in the same portion of the Sewers that Callik was originally found in. Either way, once you have the Amulet return it to Hemmel Masterson to complete this quest.