If you have a website, or even just an profile page on a site where you can add a little html, go put a link to your Mastodon account with the attribute rel="me" there.
For example:
<a rel="me" href="https:/ /your.mastodon.server/@yourhandle">Mastodon</a>
Then, in your Mastodon account, go to Preferences > Profile > Profile Metadata, and add a link to the page where you put that html.
For example:
Homepage https:/ /yourwebsite.com
That's the easiest form of verification on Mastodon.