I assume you added an ePub file to iBooks.app on your iMac and added highlightings there.
Yes, you can in fact sync your highlightings/notes/bookmarks between multiple devices running macOS and/or iOS.
Please follow these steps to sync your highlights:
- On your iMac go to
System Preferences > iCloud.
- Make sure that you are logged into your iCloud account. If not, log in.
- Depending on your version of macOS you need to check the check mark for
Documents & Settings.
In iBooks.app sign in to the same iCloud account it you aren't already.
Make sure that the ePub file is the very same on both Macs.
Prepare your MacBook
- Repeat the steps above that you did for your iMac.
Sync your highlightings
- Reboot both Macs
- Open the ePub in iBooks.app on your iMac and add a note or a bookmark.
- Close the ebook in iBooks.app but leave iBooks.app running.
- Open the ePub on your MacBook with iBooks.app. Wait for the highlightings/bookmarks/notes to appear. It may take a few minutes for the first time.
- If they don't appear on your MacBook, add a new highlighting/bookmark.
If possible, you should run the same versions of macOS on both Macs. Also check for available software updates.
Using the same Apple iCloud account is necessary for the synchronization to work with Apple's iBooks.app. You can't use another cloud storage provider for this.
Unfortunately there is no other way to sync them other than to re-add your edits by hand.