A graduation speech from Holden Caulfield in the novel "Catcher in the Rye" by J.D. Salinger would make very interesting listening! I think he would start by making a very very long tribute to Allie, including all attributes, personal qualities and ideas of integrity that he perceived Allie as having. I think he would make a big deal out of how Allie wasn't a phoney and then might go on to say how all the people listening (school administrator, teacher, peers, fellow pupils,parents) are all fake compared to Allie. Then Holden would probably want to praise his sister Phoebe and wish her well, but maybe either ignore or criticize his parents. He might use the opportunity to settle a few old scores with Stradlater and other people who bugged him in school. Most of all, I think he would wear his red hunting cap!
This is a fairly interesting task. It certainly would be "interesting" to hear Holden address his colleagues. Outside of the personal disdain he would hold for him, I do believe that he would offer some strong caution about avoiding phoniness and in-authenticity. Holden would speak to the notion of maintaining personal integrity and identity as the circumstances that present themselves might force individuals to compromise on these elements. At the same time, I think that Holden would speak of a world that can be transformed into something better than what it is. To this end, he might invoke Phoebe as a closing symbol of how thing can be. Holden's devotion to his sister might be an appropriate note for all graduates to find their own passion, their own voice, and the end to which they would commit themselves in order to find meaning in the world.
It amuses me to think that any school administrator in his/her right mind would ask Holden to give a graduation speech. However, I can imagine that if this very strange choice for a graduation speaker were to occur, Holden would have some pretty sarcastic and negative things to say, i.e.:
Hey, you morons! This place, Pencey Prep, is full of phonies. I don't know why they asked me to speak, since I flunked out of this place four times, but what the hey. I see some of my so-called friends sitting in the audience. There's "old Robert Ackley" over there, still covered with zits. And, hey, "Old Stradlater" - dude! I never did write that paper for you so you could go out with Jane. But I'm not sorry.
"If you really want to hear about it," ............
You get the idea. Go through the novel and pick out some of Holden's more colorful assessments of his time at Pencey and his evaluations of his "friends" there, and you can put together a graduation speech.
Another approach would be, assume that Holden actually is healed at the end of the novel (although we don't really know this), and have him give a graduation speech based upon the lessons he has learned from being a messed-up teenager.
See the analysis here on enotes for help.