You could go about this answer in two different ways.
First, you could scour the text for examples of direct characterization, because those bits of text will tell you exactly what character traits that Jonas has. For example, chapter 1 tells readers that Jonas obediently follows the rules of society. We are also told during his ceremony that Jonas is intelligent, is courageous, is wise, and has integrity. He also has something called the "Capacity to See Beyond."
Second, throughout the text, readers can find indirect characterization examples that support those character traits. For example, Jonas shows courage when he intentionally leaves the community with Gabriel in order to save him from release and fight against the Sameness. This also shows that Jonas is selfless. He is putting himself at great risk for Gabriel and the rest of the community. He has a strong moral compass because he is willing to do what is right to fight the Sameness and bring back diversity and choice to his community. Jonas also has perseverance. We don't know what happens to Gabriel and Jonas at the end of the story, but we do know that Jonas refuses to give up.