All Treasures in Chapter 10 in Resident Evil 4 Remake

CQBR Assault Rifle: This weapon also counts towards treasure/weapon trophies. Remember when you played as Ashley and lowered stairs in the south part of the library? Use the Cubic Device on the Square Lock Box up there. If you don't recall, head to the library, go south, walk west around bookcases to find the stairs. The box is in the room at the top.

Golden Lynx: From the library, go to the room with the typewriter (via elevator or hallway to the right of it, where Ashley found the clock shortcut). The Golden Lynx is inside a Square Lock Box in this room.

Ruby: Progress the story until you reach the large circular Ballroom area. The Ruby is in a silver container hanging under the rubble to the right of the stairs on the lower floor.

Ornate Beetle: In the same Ballroom area, on the lower floor, walk along the northern edge. Go through the area with wooden scaffolding and a ladder. Continue past the ladder to find a treasure chest behind it containing the Ornate Beetle.

Elegant Crown: Progress until you reach the Depths area. Head towards the room at the back. Go to the right side of the room and forward to a dead end. The Elegant Crown is on the floor next to a corpse, near the Prisoner Notes file. This is just after the gap you can create to enter the room.

Red Beryl: In the Depths area, break a nearby wall to create a gap to enter a room. Climb a ladder and walk through a tunnel to an alcove on your left. Look up to find a silver container hanging above; shoot it to release the Red Beryl.

Yellow Diamond: Continue from the Red Beryl location until you find the Merchant. After the Merchant, keep heading west. You'll find a small underground lab-like room with an elevator. The power to the elevator is in the far west corner. Head west to a room to your right. Go through a small gate and use a switch to open a large gate. After passing through, you'll be attacked by a tendril. You need to turn on the power to get the treasure. Head to the power switch while avoiding attacks. After pulling the switch, you may initiate a boss fight with Verdugo. You can defeat Verdugo for the 'Wave Goodbye, Right Hand' trophy/achievement or bypass the fight and wait for the elevator. Regardless of your choice, head back to the switch that opened the large gate. The wall blocking the treasure will have moved. The Yellow Diamond is in a chest next to a First-Aid Spray.