Cisco ASA show VPN users

To find out remote clients connected to Cisco ASA Firewall, use the command:

sh vpn-sessiondb remote

There are other useful options for this command, such as:
sh vpn-sessiondb l2l --> for IPSec L2L connections
sh vpn-sessiondb svc --> for SSL and anyconnect connections
sh vpn-sessiondb webvpn --> for WebVPN sessions

If you are looking for a specific user, use the following command:
sh vpn-sessiondb remote filter USERNAME

The option exists for l2l, svc and WebVPN as well.