Quid agis, Quomodo
What's the difference between quid agit and quomodo?? They both are "how" in one way or another. But which one for what use?
Nothing technically, it's all about that grammar and them idioms.
Quid + agere literally means what are you doing?, but is used in a broader sense of how are you doing? kind of like "what's up?"
Quomodo x + habere is How does X consider themselves (to be)? a sort of, "How do you think you're doing?"
You can use both at your leisure. Just know that a lot of people try and use sum, esse plus adjectives for that kind of thing, which isn't as typical. Latin has a wealth of verbs for answering those types of questions. Like esurio I am hungry