Hi mrstella,
Please follow the steps in the link below to learn how to sync audiobooks to your Apple Watch.
Add audiobooks to Apple Watch - Apple Support
Next, we’d like to show you how to perform the recommended troubleshooting steps via the link above. Please click to open the link, then read through the steps in the section below.
1) Open the Apple Watch app on your iPhone.
2) Tap My Watch, then tap Audiobooks.
3) Tap Add Audiobook, then select audiobooks to add them to your Apple Watch.
If there’s available storage space, the entire contents of the audiobook you’re currently listening to—as well as the one listed below Want to Read—are automatically synced to your Apple Watch. 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.
The reason why we are recommending the steps above is because they will show you how to Add audiobooks to your Apple Watch.
Please let us know the outcome after giving the above steps a try.
Thanks for using the Apple Support Communities.
Cheers!