nslookup is a program used to manually query DNS servers.
An example query:
$ nslookup -sil wiki.linuxquestions.org Server: 192.168.1.1 Address: 192.168.1.1#53 Non-authoritative answer: Name: wiki.linuxquestions.org Address: 220.127.116.11
Server and Answer describe the server asked. Name is the host we have asked about and Address is its IP address
Note that I have used the -sil flag, because it supresses the message that nslookup is obsolete.