A book title cannot technically be protected under trademark law, unless it is the title for a series of multiple books. See TMEP §1202.08.
But that doesn’t mean that an author cannot use a or phrase that he or she have registered as a trademark for other services to also serve as the title of a book they wrote. It just means that technically the use as the title is not protected to stop other book titles.
But having a trademark associated with the book title is useful when possible, because it will help you control the relevant domain name(s) and social media profiles. And it will be in the public records at the USPTO. And it will mean that others are less likely to use the name as their book title (even though they might technically be able to under the law) if they will have trouble promoting it because of your use and registration of the name for other services (such as a blog, information website, seminars, consulting, etc).
In addition, if you write a book and the title is separate from the trademark used to identify your services as a professional or expert in a field, you can still use and promote your trademark on the book. See for example these uses on the backs of two book to promote the authors’ brands, Mr. Media Training® and LawBiz®:
Disclosure: Ed Poll is friend, Brad Phillips is a friend and a client!