I found a similar question for many other languages - ASP.net, Django, etc... However, I am interested in Express.js over Node.js . How can I view all the sessions that are currently active?
I would look into the store you use for session data, unless you use cookies to actually store all session data, not just the session id.
Maybe there is a way to access the list of sessions regardless of where you store session data, but I think that there isn't. But I might be wrong here.
Express Session API is described here, in case you couldn't find it (I spent a lot of time to figure out that many Express objects are actually Connect objects and documented there). But you probably knew it...