Jonah was arbitrarily virtuous. When he was younger, his mother always told him, "That's gonna screw you over, Jonah." though, Jonah never paid any attention to this and continued being the same. People called him naive or shallow for such things, "the willingness to help random people could get you killed you know!" Someone had told him that before, and even then he couldn't remember who it was.
It was a part of his simple nature just as much as being kind; he was forgetful. Because of this he often forgot about people who he wasn't close to, or didn't interact with often. He would constantly forget the "words of wisdom" from his father, and even forget the advice his mom gave him, even if he wanted to take it. Despite this education wasn't especially difficult, Jonah excelled in math over other things because other subjects took more memorization, whereas with mathematics you wouldn't need to memorize as much. Numbers and statistics just came naturally to him.
When it came to making friends or acquaintances, Jonah was great at it, or evening mediating other conflicts for people. Because of his kind nature, he was able to become friends with Mono, who at first seemed like a mysterious man. Later on though, he found out Mono was just a struggling older brother. He was also the first person aside from Mono that Grey opened up to, really Grey could confide in him for anything.
Despite all of that, being an imperial soldier, Jonah had access to all types of information. He was lower ranked, but that did not mean disrespected. Jonah stood atop of his peers as an outlier because of his immaculate physical strength. His kind nature and being easy to talk to allowed him to make connections with higher ups aside from his military prowess. This was when Jonah finally learned the truth about Grey. He understood what his situation was, what type of past he had led. He wasn't so sure Grey really did have amnesia. Although all of this was going on he still managed to lead a happy life with his friends and his fiancee. Though shortly after this was disrupted by meeting Lucian, who forced it onto him. Even on his deathbed Jonah tried to dig deeper, to find out more–
Hey man, can't tell you more than that.