I'd avoid physician assistants and nurse practitioners.
If you want a formal diagnosis, a clinical psychologist should have the authority to assess and diagnose ADHD. A psychiatrist can, too. The best way to approach getting a diagnosis (and the finer detail of what kinds of psychologists can do a formal diagnosis, what referrals you might need, etc.) is highly dependent on location. Once you have a diagnosis, you should be able to try medications if you want.
If you aren't interested in medications, you might still want to pursue some (enough for you to learn about yourself) or all of a formal diagnosis if you want. The benefits and downsides of a formal diagnosis are also highly location dependent.
Talking to a psychologist might be helpful regardless of diagnosis.
Please don't use an ADHD 'coach', they're a predatory scam
If you want a formal diagnosis, a clinical psychologist should have the authority to assess and diagnose ADHD. A psychiatrist can, too. The best way to approach getting a diagnosis (and the finer detail of what kinds of psychologists can do a formal diagnosis, what referrals you might need, etc.) is highly dependent on location. Once you have a diagnosis, you should be able to try medications if you want.
If you aren't interested in medications, you might still want to pursue some (enough for you to learn about yourself) or all of a formal diagnosis if you want. The benefits and downsides of a formal diagnosis are also highly location dependent.
Talking to a psychologist might be helpful regardless of diagnosis.
Please don't use an ADHD 'coach', they're a predatory scam