Reading good Enneagram books is helpful in giving you good knowledge about the different type descriptions and their associated mental and emotional patterns. You can use these information for self-reflection.
Some books also include checklists to help you identify your type. So if you are more like a typical type, you can figure out your type quite easily based on the descriptions. But if you belong to those variations of the type, you will have a harder time.
Books by Leading Enneagram Authors:
Enneagram Books written by Don Riso & Russ Hudson
Enneagram Books and Publication by Helen Palmer & Associates
Enneagram Books in Business by Ginger Lapid-Bogda & Associates
Ennegram Books in Spirituality by Sandra Maitri