There are regular surveys, and then by talking to people on events, conferences or just by people providing feedback on one of many channels. And of course by statistical measures such as traffic, editor activities, etc. (for which WMF has team that does relevant data collection and research - yet another non-obvious place where people work that is not directly "site maintenance"). You can also check out https://www.mediawiki.org/wiki/Collaboration and https://meta.wikimedia.org/wiki/Community_Resources for teams that do it and know better than I do :)