In the Great Gatsby, what is Nick's "journey of enlightenment"?

Right - to complete the above answer, in the beginning of the book, Nick is young and immature and just starting out in life. Then he meets Gatsby and looks up to him so much, really idolizes him. He hears about Gatsby and Daisy and feels so special to be a part of bringing them back together. Then things begin to fall apart. He learns the source of Gatsby's wealth, Daisy runs the woman over with her car, Tom and Daisy's callous disregard for both human life and love and what is right and responsibility, and finally no one comes to Gatsby's funeral after every one had shown up to all of his parties. Nick is able to see that in the end Gatsby's dreams killed him, and all that Nick thought was ideal was actually low and dirty and not good, and he has learned a lot about human nature and society.