Indonesia Etc.: Exploring the Improbable Nation by Elizabeth Pisani (2014) — The best modern overview of Indonesia's improbable diversity. Pisani travels through remote corners of the archipelago and writes with warmth, rigour, and wit. Not Cirebon-specific, but essential preparation for making sense of what you see here and elsewhere in the country.
Lonely Planet Indonesia — Reliable practical reference covering transport, accommodation, and sights across the archipelago. The Java chapter covers Cirebon with enough detail for a short visit.
The Wali Songo: Nine Saints Who Spread Islam in Java — Various editions exist under different titles; look for academic or popular histories covering the nine saints and how Islam spread through Java's existing Hindu-Buddhist kingdoms. Cirebon was Sunan Gunung Jati's base, and the context makes his tomb and the city's mosques considerably more interesting.
Batik: Fabled Cloth of Java by Inger McCabe Elliott — A thorough illustrated book on Javanese batik traditions. Cirebon has its own distinctive style: the megamendung (cloud) pattern, with its bold curved forms and Chinese influence, is unlike anything produced in Solo or Yogyakarta. The book covers regional traditions in enough depth to be useful background before visiting batik workshops.