You might need to look for specific story missions or events where the character can be shirtless. It could be part of a certain storyline or a specific interaction.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
There was a time when Paul Wesley was filming a drama series. In one scene, he had to be shirtless. While waiting for the next take, he told the story of how he got into acting. He was discovered by a talent scout at a local theater. He was hesitant at first, but decided to give it a shot. And that's how his journey in the entertainment industry began. His shirtless presence added an interesting touch to the behind - the - scenes story - telling.
It's hard to pinpoint exactly where Gojo is at any given time in the manga. His whereabouts change as the story progresses and different scenarios unfold. It could be in a supernatural realm, a mission site, or interacting with other characters.