Search Primo (the USC Libraries' catalog) for books at USC. Books specifically on musical subjects are located in the Music Library. Interdisciplinary publications, including music education and technology, are sometimes located in Doheny Memorial Library.
Books on music are classified by the Library of Congress as ML (Music Literature) or MT (Music Theory and Instruction). See here for specific distribution of subjects.
Although e-books can be found in Primo, there are also databases which contain large collections of them: