According to APA style, most book titles would be written in italics rather than underlined. This only applies, however, if the title can stand alone.
If following APA writing style is not appropriate, contact the assigning instructor to find out which style guide is preferred. Assigned reports are left up to the instructor's discretion with regard to the format and style a report should completed in. Some instructors may prefer book titles to be underlined, while others may prefer to follow APA guidelines. APA is one of the most commonly used writing styles for educational settings, and it is also used for several forms of publishing.