"What is the book that changed your life? (not novels or religious texts)"
I think it's a wonderful way to connect in a less superficial way and learn a little more about each other. It's also a wonderful way to discover new books worth reading.
This is one of them (the full list is here):
A simple yet comprehensive guide to the types of psychologies and therapies available from Eastern and Western sources. Each chapter includes a specific exercise designed to help the reader understand the nature and practice of the specific therapies. Wilber presents an easy-to-use map of human consciousness against which the various therapies are introduced and explained.