If you have wondered about that question, this is the book that will answer it for you. I have posted my review of the book on my blog, The Itinerant Librarian. Excerpt from the review:
"This novel has a great premise: what did Obi-Wan Kenobi do right after he went into exile at the end of Revenge of the Sith. The Republic has fallen, and the Empire is rising. The Jedi, what few remain, are now fugitives on the run, and Obi-Wan has to protect a young Luke Skywalker. With the Empire consolidating power, out of the way Tattooine is a perfect place to hide, or so one would think."
Read the full review by clicking on the link: http://itinerantlibrarian.blogspot.com/2013/09/booknote-kenobi.html