While the focus is in one of the SQL Commander tabs you'd like to duplicate, either right-click the tab header and choose New SQL Commander or use the associated key binding with that action, typically ctrl+t on Windows.
This will open a new SQL Commander with the database connection, schema, database and other settings set.
This is a feature request. I usually have multiple SQL Commander tabs open at once that are pointed to different database instances. It would be neat if I could right-click on a tab and have an option to duplicate all of the attributes of that tab into a new tab. This would be helpful for when I'm working on and testing multiple versions of a complex query. It would save some 'clicks'.