Between the title and subtitle of a book, the correct punctuation mark is a colon.
The following rules apply only when the titles are vague or not clear. First, a title having two subtitles, use two colons in separating them. Second, a period separating a title and a subtitle, change the period to a colon. Third, a title ends with a question mark or exclamation point, retain the mark or symbol and add a colon to separate the title from its subtitle.