When Truman abruptly crashes into the wall of the studio. Feeling that he is trapped forever and understanding how his whole life was a lie, he begins to break down in tears as he tries to punch through the wall in a futile manner. The lack of sound in this particular shot makes it just that much more soul-crushing.
Truman being reunited with his (actor) dad as part of a ploy of Christof's to keep Truman on the island. While Christof is manipulating the scene with rising music and dramatic shots, the real, genuine emotion of Truman at once makes the scene work In-Universe but also for the actual audience in terms of dramatic irony, how Truman is just a part of the emotional pandering itself, without his knowledge.
The scene where Truman and Marlon are sitting on the bridge and Truman's talking about his fears and suspicions. Getting his lines fed by Christof, Marlon tells him to trust him, that he would walk into moving traffic for him and then pauses before saying that he would never lie to Truman. You can tell from his face that he feels terrible about doing this to Truman.
Look closely at Truman's face. He's not crying because he's so moved by Marlon's speech, he's crying because if "everyone" is in on it, Marlon is, too. AKA, his best friend since he was seven years old. Sheesh.