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