Evil West

Perks are combat moves and abilities you unlock by spending perk points you gain each time you level up. The maximum cap is 30, so you will earn 30 perk points plus two more hidden in chests to choose between 36 moves and abilities. These perks are accessible as you reach certain levels; however, eight are in the hidden chests you need to find to unlock them with perk points. This trophy is only related to finding those eight perks; you don't need to unlock them from your Perk tree.

In the lore tab, you can see how many hidden chests are in each chapter, but it doesn't tell you which ones contain the hidden perks and which contain other items, such as character skins, weapon upgrades, and Perk points)

Chapter 02 - The Raid - 1 Chest (Ghost Scarf - Skin)
Chapter 05 - The Devil's Pass - 2 Chests (Ghost Rifle - Skin & Booming Business - Perk)
Chapter 06 - Remote RI Outpost - 2 Chests (Ghost Suit - Skin & Lethal Heights - Perk)
Chapter 07 - Smoke and Mirrors - 2 Chests (Ghost Hat - Skin & Boom Balls - Perk)
Chapter 08 - Pharmakon - 1 Chest (Adrenaline Junkie - Perk)
Chapter 09 - Where Oil Tastes like blood - 3 Chest (Ghost Boomstick - Skin & Perk Point & Bursting bolt - Upgrade)
Chapter 10 - Bats in the Belfry - 1 Chest (Healthy Lifestyle - Perk)
Chapter 11 - A Man of People - 2 Chest (Work-life Balance - Perk & Gun Revolver - Skin)
Chapter 12 - Lightning in a Bottle - 2 Chest (Ghost Gauntlet - Skin & Perk Point)
Chapter 13 - Old Friends - 1 Chest (Life Support - Perk)
Chapter 14 - A Son's Duty - 2 Chest (Ghost Zapper - Skin & ToolDown - Perk)
Chapter 15 - The Heist - 2 Chest (Fire and Forget - Gatling Upgrade & Perk Point)

For the video guide on their exact location, check out Chest Nuts