Go to Your WHMCS Directory
=> Includes Folder
=> Download Whoisservers.php File
=> Open that file in Dreamweaver, notepad or any Editor you Like.
=> Add below lines

===
.pk|http://pk6.pknic.net.pk/pk5/lookup.PK?name=|HTTPREQUEST-Domain not found
.com.pk|http://pk6.pknic.net.pk/pk5/lookup.PK?name=|HTTPREQUEST-Domain not found
.net.pk|http://pk6.pknic.net.pk/pk5/lookup.PK?name=|HTTPREQUEST-Domain not found
.org.pk|http://pk6.pknic.net.pk/pk5/lookup.PK?name=|HTTPREQUEST-Domain not found
.edu.pk|http://pk6.pknic.net.pk/pk5/lookup.PK?name=|HTTPREQUEST-Domain not found
.fam.pk|http://pk6.pknic.net.pk/pk5/lookup.PK?name=|HTTPREQUEST-Domain not found
.gov.pk|http://pk6.pknic.net.pk/pk5/lookup.PK?name=|HTTPREQUEST-Domain not found
===