Allow some DNS queries and block the rest

In switch command, do nothing in conditions you want to allow and block in default condition

when DNS_REQUEST {
    switch -glob [string tolower [DNS::question name]]  {         
        "*.google.com" -        
        "google.com" {        
              do nothing       
        }        
        default {        
            DNS::header rcode NXDOMAIN             
            DNS::return             
        }            
    } 
}