The DNS is not actually a database if you want to get technical ....
All of the DNS files for each of the domains on your server
are usually located in the /var/named folder on your server.
If I had a domain named "mydomain.com" hosted on the server
then the DNS file for that domain would be:
/var/named/mydomain.com.db
If you make any changes to any DNS files, you will need to restart the
DNS server process before those changes will take effect.
RESTART: /etc/rc.d/init.d/named restart
(Or you can just restart "named" from your WHM menu)