Where is the role of the Mandala clearly seen in Fifth Business?

Mandala is a Jungian concept of the self. It is a graphical representation of the center (the Self for Jung). It can appear in dreams and visions or it can be spontaneously created as a work of art. It is present in the cultural and religious representations. I'll link you with some more information on it below. The character of Mrs. Dempster is Dunstan's mandala through much of the novel. Dunstan believes her capable of miracles, and marks three - bringing his brother Willie back to life, saving him on the battlefield during WWI, and changing the life of the tramp. Throughout his life, she remains a powerful presence in his psyche.