On some npc priests.
To add the necessary prayers to your book, give your book to your instructor. He'll add the prayers you need at that time.
Sometimes using a ritual from a faith rod requires a specific prayer that your instructor won't give you. In this case, you need to give your prayer book to someone whose instructor does give that prayer, have them consecrate your book to their god and give your book to their instructor, then you can reconsecrate it back to your god with all of the prayers intact.