There are 6 Frankenstein fingers to find in the chapter.
Chapter 13-1 (Castle Hall)
When you get in the giant chess room, the finger is in the upper-left corner of the room.
Chapter 13-2 (Abandoned Wing)
After you drop down some columns, you will run on the water to reach a platform. You will then have to run to the second platform, but the finger will be waiting in between these on your right.
After you kill some ghouls while playing as Laura, you will be able to reach her back. The finger is hidden behind a wall of ice in the circular room. To reach it, use your Shadow Magic and then press + Forward with the .
This one is a pain to reach. In the circular blades room (you can’t miss it), when you pass the wheel that increases and decreases speed, go down instead of going to the left to find the finger. Please note that if you pick up the finger and then die afterwards, you DO NOT need to pick it up again.
Chapter 13-3 (Founder’s Quarters)
When you complete the puzzle on the floor (align the circles), go down the stairs and then to the left to find the finger.
When you must collect the three blood orbs, you will reach a hall with three different paths. Take the left one and the finger is hidden behind a breakable wall on the right.