Hey,
There are a few ways to list and kill sessions in the Denodo Servers.
With the new Diagnostic and Monitoring tool, you can add the server to your list, logged in as an admin user. When you open the server a new dialog will open, and you can go to the Sessions tab and right-click > Cancel Connection for any of the sessions. I don't think this is available in the Denodo Express edition.
Another way is using an JMX agent such as Java Visual VM or JConsole, which come with every Java Development kit. You can use these to connect and monitor the MBeans coming from a Denodo Server.
For example, the VDBServerManagementInfo MBean for the Virtual DataPort, has commands for getSessions, closeConnectionById, closeConnectionsByIP and closeConnectionsByUser. The first one will list the sessions, and the latter functions will kill sessions based on the parameter described.
The MONITORING WITH A JAVA MANAGEMENT EXTENSIONS (JMX) AGENT section of the Denodo Virtual DataPort Administration Guide has a lot of information on how to utilize MBeans.
Finally, if you would like to stop a certain query that is running, you can go to Tools > Query Monitor in the Administration Tool. This will provide a table of the current queries being processed, and you can click on a Query in the table and click the Stop button to kill it.
Hope that Helps!