Toward the beginning of the novel, Jonas struggles to put into words his feelings about the upcoming ceremony (where he will turn 12 and get his job assignment). On page 4 in my copy (chapter 1), it says: "But there was a little shudder of nervousness when he thought about it, about what might happen. Apprehensive, Jonas decided. That's what I am."
In chapter 8, Jonas expresses his fear when he realizes he was skipped in the assigning ceremony. It says, "Now he felt only humiliation and terror" on page 59 of my copy.
During the escape, Jonas expresses fear in various ways; fear of being caught, of starving, of not being able to save Gabe.