This is a tough question to answer, as it's a vague topic to write about. What are you supposed to be reflecting on as Holden? Himself? The events of the book? Other people he meets? His mental state?
The key to remember about Holden is that he sees things from a skewed perspective. He does his best to make himself look good, and to make others look substandard, according to the criteria he sets--criteria that is constantly changing based on his moods and whims. Holden consistently criticizes those people and things around him that he considered fake or phony, which are most things (with the exception of Jane, Allie and Phoebe). He doesn't want to admit to liking anyone or anything because, if he does, he gives those people or things a chance to leave or hurt him--and he'd been hurt enough by Allie's death.
If it were me, I would write the essay as if Holden has figured out all the things we want him to figure out. Such as taking responsibility for his life and his choices. His shortcomings cannot always be blamed on other people.
You could write about how Holden felt about events from the book. Sure the book is in first person point of view and we are able to see how Holden sees events, we never know what he is actually feeling in scenes. Most of his emotions and ideologies are inferred based symbols and words used in the specific scene. There would be a lot to write about if you choose to write things from his emotional prospective.