However such information isn't always available. The domain may have privacy protection enabled to keep this info hidden to prying eyes. In some other forums you may find the information, but the owner of the domain might not be the owner of the forum, i.e. when the forum is under a free forum hosting services housing tons of free forums. Your first try should be looking somewhere in the footer for the contact details, or "about" page that sometimes have some of the info you are looking for.
Submit a ticket at their help desk or whenever you register there might be contact info and you can search on whois.com