It's in the locked chest (Stealing). Lock level 5. It can be unlocked with Takano's Key.
Others, Neketaka, Serpent's Crown
Locations on Neketaka, Serpent's Crown
1
Cornett of Waves
Related quests: The Cornett's Call
2
Lady Epero
Related quests: Bounty - Lady Epero
Lady Epero + 2 x Mercenary Swashbuckler + Mercenary Wizard + 3 x War Dog.
3Muhai's Remains
Related quests: Her Last Request
It's in the corpse.
4
Takano's Key
It's in the armoire (Stealing).