The Volunteers tab is located on every channel and video page and lists the users that have worked on that particular channel. This section can be found by scrolling down on any channel or video page and selecting "Volunteers."
Users are listed by role (e.g. Channel Manager, Moderator, Segmenter and Subtitler). Hovering over a user's profile picture will show you more details regarding their role (ex. the specific language they moderate or the number of segments or subtitles they've created on the channel).