This article is to retrieve the User information without logging in to the GUI (management page) on the browser. Active and inactive user info will be displayed.
To know the status of users logged in using User-level authentication and/or VPN on the GUI is found under Device | User | Status page after you log in.

In CLI mode, after you successfully log in using any terminal application, run the following command:
> show user status
In the below example, I'm using puTTY to login to SSH or console access for CLI. There are 3 active users. User1 is the active SSLVPN user and 1 NSM admin user and the other admin user in config mode.

NOTE: Config mode is not required to pull the user status info
There are also more details like IP address of the user, how it got authenticated, the user group and privileges, and active session time.