You can retrieve all the IP addresses of connection attempts from the web portal in the "rdp_log" file located in "C:\Program Files (x86)\TSplus\Clients\webserver" .

Then filter the lines containing "HTTP > HTML5". You won't have either any usernames or computer names.

However RDS-Knight should help you. RDS-Knight will secure your server by blocking unwanted connections.
In the RDS-Knight "Event Viewer" you will see all the connection attempts, displaying the IP address AND the username.

RDS-Knight is available for TRIAL testing at this address: