1)I am sharing internet through proxy server

what should put in the ip of the dns server tho use dig command, whether i should put address of proxy server or the address of dns server

dig @DNS_server host

and when i tried with dns server ip it says,
# dig @172.16.0.1 www.linuxquestions.org

; <<>> DiG 9.2.3rc2 <<>> @172.16.0.1 www.linuxquestions.org
;; global options: printcmd
;; connection timed out; no servers could be reached

and when i tried with proxy server ip it says same thing as above.

#/etc/resolv.conf
nameserver 127.0.0.1
nameserver 192.168.1.2
nameserver 172.16.0.1


2)# nslookup www.linuxquestions.org
Note: nslookup is deprecated and may be removed from future releases.
Consider using the `dig' or `host' programs instead. Run nslookup with
the `-sil[ent]' option to prevent this message from appearing.
;; connection timed out; no servers could be reached

how can i run nslookup command

Well no one could possibly know what DNS servers you have available. You have to find out from your system administrator what IPs to use for /etc/resolv.conf. If you've setup your own network, have you also setup a DNS daemon? If so, did you configure it to allow recursive queries? Have you setup a firewall?

thanks chort for your response,

I am not asking you my dns server address

for using dig command, what should i put into the dns server address

either

1)whether i should put address of proxy server

2) or the address of dns server

becz i am accessing net through the proxy server.

You must put your ISP's nameservers in /etc/resolv.conf if you don't have your own DNS.
Also in dig or nslookup (even if it's deprecated) you must supply a valid DNS IP address. So use again your ISP's DNS.
Those 192.168.x.x and 172.16.x.x are private IPs used in lans and not in public, so you have to be sure that there are nameservers running at those IPs at your lan.
If you access the net through proxy, then the box that runs the proxy server must be configured with valid DNS entries.