There are a number of ways to check this, however, we find the most reliable to be a simple ‘whois’ check.
The tool we use most commonly is…
http://whois.domaintools.com/
Or, if you are using a Linux machine…
yum install whois
Then, you can run the following…
whois domain.com
Important: Some people, including many registrars will recommend you find the relevant nameservers of a domain via a DNS lookup, such as whatsmydns.net – this is incorrect.
The NS records that sit within the DNS zone, do not always match those sat at the registry of the domain. The only reliable method to find the nameservers being used, is via a WHOIS search.
The reason we recommend the above method, is that this checks directly with the Registrar. DNS Zones are prone to errors, and can, therefore, reflect an incorrect value.