At the end of Chapter 7 in Call of Cthulhu, called the Nameless Bookstore you will encounter a safe that you need to open in order to push the story forward. To open the safe, you need to set the right combination - you can find it when exploring the bookstore itself.
After the reconstruction with the safe finishes and you retrieve control over your character, approach the bookcase to the right from the safe. Between the books, you will find the Drake's Memories in which you'll find clues on how to open the safe.
Return to the bookstore's main room and go towards the last bookcase isle. You will find a board you can interact with - behind it, there are two new Drake's Cylinders (2 and 3). Now, go to the small room located next to the bookstore entrance.
Approach the stack of books by the window and investigate the Goblet. Now, check the chessboard set on the table, and finally approach the phonograph and listen to all recordings from the cylinders, as they include the clues on how to open the safe:
- Cylinder 1 - Cylinder 1 - regards the Goblet from this room. Indicated number 5.
- Cylinder 2 - regards chessboards on the table and the chess pieces defending the queen. Indicates number 3.
- Cylinder 3 - regards the books you can find on the counter and to the total amount. Indicates number 9.
Now go to the sage and set the right combination: 5, 3, and 9. Accept your choice. This will activate a cutscene, after which the chapter ends.