Open a Book (that was updated) in the Kindle app: Flip a page or 2: Exit back to the 'Library'
Now open the
My Kindle Content folder using the OS:
Sort t hat on the
Date Modified (list view) The MBP files
NAME was the last viewed Book (

F5 when the window is active, refreshes the list)
You now know what title. Repeat as needed, 1 cycle at a time