Assuming you're referring to Server license and assuming you're an Admin, on your Server page, you might've already looked at this but there should be a "Users" tab. Click on that and it should have list of all the Server/Site Users, user names, roles and last logged in information. Sort "Last Logged In" info to identify users.
I'd recommend taking advantage of Matt Coles efforts: Tableau Server Insights (formerly Shareable Data Sources for Tableau Server)
His work takes care of all of the connections and dimension/measure labeling.