Transfer audio book from iPad to Mac
Before you transfer your purchases, make sure that your MacBook is authorized with the same Apple ID account you used to make the purchases. 
And for audio books, only one download is normally allowed per purchase. You can find the answer in Apple support center. 

To transfer purchases from your device to a computer:


Connect your device to the computer. Wait for its icon to appear in iTunes.
Go to File > Devices.
If you're using iTunes for Windows and can't see the menu bar, learn how to turn on iTunes menus in Windows.
Choose Transfer Purchases from [device name].