you can connect to a WHOIS server and query it with "data-extreme.com" the WHOIS server will give you the list of name servers, is this what you want? it would give you this:

NS1.DATA-EXTREME.COM
NS2.DATA-EXTREME.COM

or if he has a static IP which he should, you can do a reverse DNS on the domain name, which will tell you the IP of the domain name, and if the IP matches his static IP then its registered to his DNS, if it doesnt match its not - i thnk this would work