Book: The Message of Jonah
If you’re after a commentary on Jonah (a book that a scholar has written that explains what they think the book means), this is a good place to start. It’s not too heavily academic, but it contains reference to a lot of what has been said. If reading 200 pages on a book that has 48 verses seems too much, you would be better off starting with a whole-bible-in-one-volume commentary instead.