Start with high-confidence comparative religion books, then narrow by subgenre or adjacent topics.
My Jesus Year
Benyamin Cohen
The Kingdom of the Occult
Walter Martin, Jill Martin Rische
A Concise Guide to the Quran
Ayman S. Ibrahim
Living Buddha, Living Christ
Thich Nhat Hanh, Elaine Pagels
World Religions: a Beginner's Guide
Jill Carroll
