Add audiobooks to Apple Watch
Open the Apple Watch app on your iPhone.
Tap My Watch, then tap Audiobooks.
Under My Library, tap Add Audiobook.
Select audiobooks to add them to your Apple Watch.
By default, the next five hours of the audiobook you’re currently listening to, as well as the one listed under Want to Read, is automatically synced to your Apple Watch if there’s enough storage space. Five hours from each audiobook you add is also downloaded to your Apple Watch when there’s available space. Audiobooks sync to Apple Watch when it’s connected to power.