External Invigilator Told Be to implement MITM ( Man In The Middle ) for a project

I presented my minor project on a Network Packet Analyzer built in Java that captures and analyzes TCP/UDP/HTTP packets from your own device, including traffic flow visualization. During my final defense, the external examiner asked if it could capture packets from all network devices. I replied no, and mentioned a proxy server would be needed. The examiner then told me to implement that and return.

Now I am researching and suspect he meant a "man-in-the-middle" setup, but I'm unsure how to do it or whether it's even legal, especially since I'm not from a cybersecurity background. You're looking for guidance.