How SQL Developer Monitor Sessions

To monitor sessions in SQL developer, you may find the entry in the function menu of "Tools".

SQL Developer - Tools - Monitor Sessions

Then select which database you want to connect to and monitor.

SQL Developer - Choose Connection

Right-clicking on any one of sessions shows a menu, there're more actions you can do on it, which include killing the session.

SQL Developer - Kill Session

There're more various session monitorings in "Reports" panel. The navigation path is as below:

All Reports > Data Dictionary Reports > Database Administration > Sessions

SQL Developer - More Session Monitoring

You may take a look.