Structure of the Book of Job (David Dorsey, The Literary Structure of the Old Testament: a commentary on Genesis - Malachi, p. 170)
A. ch. 1-2, Prologue
B. ch. 3, Job's challenge
C. ch. 4-27, Job and 3 "friends"
D. ch. 28, Wisdom
C'. ch. 29-37, Job and one more "friend"
B'. ch. 38-42:6, God's answer to Job's challenge
A. ch. 42:7-17, Epilogue