The Stinky Scale is an old Adventurer's Tome in Lost Ark. You can usually only get it on the Tortoyk Continent, where it sometimes drops randomly.
Where is the Stinky Scale in Lost Ark?
We have found that the Stinky Scale drops more frequently when fighting the larger monsters in dungeons. The best way to increase your chances of getting the Stinky Scale is to go straight for the special monsters.
You cannot earn these collection items in a set way; you earn them as random drops for killing monsters. Even though the item supposedly grows from pirates, it will look like a blue scale from a fish.
It is best to place it in a secluded, safe place before putting it in your own Adventurer's Tome. Mokoko Village is usually the best choice, since it's the only spot where you will be completely safe.
Open your Inventory by pressing the I key and then right-click on the Stinky Scale. You will receive a notification that the Stinky Scale collection has been added to your Adventurer's Tome.