How to find IP address of a DNS server

Question

I'm a CS student and currently taking a (basic) course in information security. I was given an assignment which required me to analyse a given .pcap file using Wireshark and obtain information on the host's IP address, browser, router's MAC address etc. One of the questions required me to determine the IP address of the DNS server which the host uses, but I'm not sure how to do that. I've seen websites that tell you how to find the IP address of the DNS server used by your own router, but how do we find the IP address of the DNS server another person uses, given that we know the MAC address of his or her router?

Solution

I would assume that if you have a pcap of traffic from the target host, you could determine the IP address of the DNS server by looking for open connections to a destination IP on the DNS port (TCP/UDP 53).