Courtesy of Chris Galea:
Enneagram, NLP and more
Not a book but very much worthy of a place in the Library - whilst Enneagram led, the content has much broader applications and deeper learnings for your client work.
A very interesting conversation between Katherine Fauvre (Queen of TriTypes and Instinctual Stacking plus so much more), and Tom Condon (King of NLP, author of over 50 books on Enneagram) cover a range of topics and deliver some fascinating insights that will definitively impact your application of this approach.