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.