All Treasures in Chapter 9 in Resident Evil 4 Remake

Depraved Idol: At the start of the chapter, backtrack to the Wine Cellar. Turn right, go through the door into a room with Knight Armor enemies. Defeat the attacking Knight, then head to the eastern gate. Look up to find a hole in the wall; boost Ashley through it to unlock the gate. Enter the room, open the chest to collect the Depraved Idol, and pick up the file to the right of the chest.

Elegant Chessboard: Return to the Courtyard. From the entrance, head east, ignoring the first left near the stairs. Take the second left (north), follow it around the corner east, then head north to the next intersection. Turn east and follow the path to a small room containing a treasure chest with the Elegant Chessboard. Be prepared for plaga-infested dogs that will ambush you. Flash Grenades and the TMP gun are recommended.

Alexandrite: In the Grand Hall, locate the Merchant's room. To the right of the Merchant's room is a statue holding a silver container. Shoot the container to obtain the Alexandrite.

Small Key: After obtaining the Alexandrite, head up the stairs in front of you and turn left to reach the upper balcony. Follow the balcony to the back and enter the door to your right. Continue through the hallway until you reach the next room. The Small Key is inside a set of drawers in the northwest corner.

Cubic Device: Progress the story until you reach the Armory. After dropping into the room below to retrieve a statue head, you will be ambushed by Knight enemies. Defeat them by aiming at the plagas emerging from their necks. After the fight, catch Ashley to help open the door. Go through the door and follow the hallway to find a chest containing the Cubic Device.

Yellow Diamond: Enter the Gallery room via the door on the southern balcony in the Grand Hall. Deal with the numerous enemies, including a Summoner on the balcony at the back. Rush the Summoner to prevent them from transforming enemies. You may need to shoot a fire lantern above shield guys to defeat them or use grenades. Climb the ladder to the back balcony, defeat the Summoner, and use the nearby lever to raise the bridge. The treasure chest containing the Yellow Diamond is on the bottom floor, under the raised bridge, nearer to the entrance.