Hi WoodyZ,
okay, I spent a lot of time for this question but at the end it seems that the DNS requests of a virtual machine are not logged for later investigations. At least in a default host configuration. The command sudo killall -INFO mDNSResponder prints only the current state to the syslog. If you run sudo killall -USR2 mDNSResponder insteada detailed packet logging will be enabled and each DNS request is logged in system.log but the mystery is that only host requests will be logged. If I work on guest machine no further information's are logged in the host system.log. So it seems that there is a difference between processing or to hand over a DNS request.
Thx & Bye Tom