I just did a search for that myself and of the several I lent, the most successful was Rome Sweet Home by Scott and Kimberly Hahn. Its intriging to a Protestant - particularly a non-denominaional born-again - why anyone would want to be Catholic. The reasons are here, and you get to follow along with the author’s discovery! Its a page-turner. This is the book that changed me and also is moving a close friend fo mine. For someone with a perhaps shorter attentions span, along the same lines is Surprised by Truth. There are a variety of similar stories of conversion in it, and in each one you learn about why Catholics do that. I read "Why do Catholics do that? and lent it to my friend but it was not as intriguing as the others to her. A little too “religious” perhaps for some. More intriguing to us who already are Catholic maybe. Like reading your own family history.