Can you please guide me to where to find the "Red Book" in the APU's library?
The 'Red Book" your instructor told you about - is most likely the five volumes of large red books listing all the subject headings used for finding topics in the library of congress system. The set, as a whole, is called the Library of Congress Subject Headings. They can be one appropriate place to begin your search. You would look up your topic to determine what the subject heading or headings are for your topic and then go to APU's online library to find books and articles.
There are three sets of the "Red Books" on campus, all with the same call number: Z695.Z8 L524. On West Campus there are two sets. One set is in near the Darling Library reference desk located in the Rotunda. Another set is located in the Stamps Theological Library on the reference shelves by the call number. A third set is behind the reference desk at Marshburn Library on East Campus.
Here's the link to the record for the three sets of "Red Books" http://patris.apu.edu/record=b1032696~S32