macOS - Library Location

The following information assumes that Apple Books syncing with iCloud Drive is disabled!

Apple Books for macOS stores its data in two directories within ~/Library/Containers/.

Assets

EPUBs, PDFs, Audiobooks, etc. are stored in:

~/Library/Containers/com.apple.BKAgentService

The books and annotations databases are stored in:

~/Library/Containers/com.apple.iBooksX

The books database is located at:

~/Library/Containers/com.apple.iBooksX/Data/Documents/BKLibrary/BKLibrary***.sqlite

The annotations database is located at:

~/Library/Containers/com.apple.iBooksX/Data/Documents/AEAnnotation/AEAnnotation***.sqlite

Note that the database names will vary therefore *** is used in the filenames here.