What are the best books to learn social media marketing?
The best books to learn social media marketing (SMM), IMO, are not books about SMM. It's about copywriting and public relations. Almost all the books you will find about SMM are derivatives of these two fields of expertise.
Here are two books that will get you started in the right direction:
The Fall of Advertising and the Rise of PR by Al Ries and Laura Ries
Tested Advertising Methods (Prentice Hall Business Classics) by John Caples and Fred E. Hahn