It’s a good question. Best way seems to be NIP-05 from their own domain, or through a service provider that does a real good verification before giving out a purple check.

Reading the comments on many YouTube videos shows lots of accounts trying to impersonate the channel owner. It will probably come here too unfortunately, and the impersonators can get a check from their own domain to try to look like an official account. Something to watch out for and prepare against if we can.