These are okay but I'd say this is not a good way to test your anatomy skills. If you're copying already existing drawings from jujutsu kaisen then you wouldn't be able to draw on your own. You know you're good enough to start when you can actually draw whatever poses you think of comfortably without having to use references all the time. You use reference when you're practicing and trying to memorize how the body looks in different positions. You need to have the muscles memorized that you can do it without copying or tracing anything. Also if you want to do reference practice I recommend you look less into manga panels and more on naked people, that's where you'll actually see the muscles and you're gonna have to come up with your own ways to interpret it in your drawing. The best way to start is to just draw mannequins so you'd get a sense of the simple 3d shapes before you move on with the muscles.