I'd like to check who owns (or at least some kind of public profile page) some workspace based on its subdomain (e.g.
Is it possible?
That information is private and access to it is reserved for members of the workspace.
So if you're a member of the workspace you can find out who the workspace owner is here: https://my.slack.com/account/team
If you aren't a member of the workspace, that information is not available to you.