While any FTP user is connected to your cPanel account, their FTP connection will be listed in your cPanel File Transfer Protocol Connections area. That activity can be viewed and the connections can be terminated if deemed necessary. To see this detail and disconnect any FTP connection(s) follow the below steps
Steps to Manage FTP Connections in cPanel:
Step 1 Login to your cPanel account
Step 2 Under the section Files, click the FTP Connections icon