Because so much business is now being done online, most people will want to be able to use their proposed trademark as a domain name so that their customers can easily locate them on the Web.
The easiest way is to check if a domain name is available is at one of the dozens of online companies that have been approved to register domain names. A listing of these registrars can be accessed at either the InterNIC site or at the ICANN site. ICANN is the organization that oversees the process of approving domain name registrars. Every registrar provides a searching system to determine if a domain name is available. Type in the domain name choice and the registrar will determine if it is available.
If you find that a domain name is already taken, it's possible to locate information about the owner of the domain name. A simple way to check ownership is to use Whois.net. Type in the domain name, and the website provides the contact information supplied by the domain name registrant.
Beware that some registrants, especially those acting in bad faith, may supply false information about domain name ownership and in these cases, there's not much that can be done to track down the domain name holder.