So one of the cool features of Teams is network diagnostics. Trying to gather network information remotely from an end-user sucks. So one trick you can do with Teams is place a call to them for a while, disconnect the call, then look in the network diagnostics which will give you some decent information about the call. You get to see their network adapter, whether or not they used ethernet or wifi, their wifi signal strength, their wifi channel, their wifi band, their wifi RSSI, and their overall network statistics including jitter, packet loss, RTT, et cetera.

Article on where to find this information:

https://docs.microsoft.com/en-us/MicrosoftTeams/difference-between-call-analytics-and-call-quality-dashboard

You can look at past calls as well if they happen to call from Teams/Skype a lot.

Teams Admin Center > Users > [User] > Call History then from there you can look at the statistics for any individual participant including in meetings. The icons in the overview section are filters and the Advanced tab gives you more information.