For the most part, much of what Jonas has to endure builds to a moment of truth. His function as the keeper of memories establishes him as a character who must take action. Given the nature of Jonas's characterization, it is highly unlikely that Jonas is going to passively accept the condition in which he lives without a moment of truth forming.
This instant comes in the form of revelation. When Jonas stands on its threshold, a moment of truth emerges. Jonas understands the condition of "release" as one that means to kill. It is at this point where Jonas is no longer able to simply accept the conditions of the world in which he lives. Jonas can no longer simply accept "Sameness" as a reality and will not accept such a world. Jonas's moment of truth comes in the realization of what "release" actually means: "He killed it! My father killed it! Jonas said to himself." When Jonas comes to understand the implications of the community and what his role in it would be, Jonas approaches his moment of truth.
The need for Jonas to leave represents the moment of truth. When Jonas understands the reality of the world in which he lives and that staying means he would be a part of its machinery, his moment of truth becomes evident. This comes in the form of plotting his escape with The Giver, something that the old man understands with stark lucidity:
"Having you here with me over the past year had made me realize that things must change. For years I've felt that they should, but it seemed so hopeless. Now for the first time I think there might be a way,' The Giver said slowly."
Jonas's moment of truth comes when he recognizes that he must leave. He can no longer stay and must make an active decision to leave. Coming to this realization is where his moment of truth lies and the exact moment is his need to get out and escape from the community.
I appreciate, thank you so much, this is very helpful indeed.