"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 Four Agreements: A Practical Guide to Personal Freedom
The author uses ancient Toltec wisdom to fashion a personal philosophy around these four principles--be impeccable with your word, don't take anything personally, don't make assumptions, and always do your best. 100,000 first printing. Original.