In Opera how can I define a shortcut for cloning a tab? Currently I right click on a tab select
Assuming you mean a keyboard shortcut, go to
In the "Edit Keyboard Setup" dialogue, expand and select "Browser Window" and click the "New..." button to the right. Type your desired shortcut (space-separated, with the main key before the modifiers - for instance, "d shift ctrl", or have a look at some of the other key definitions in there, especially if you're on a Mac) in the field on the left, and the action "Duplicate page" on the right (double-click to edit a field).
Once you've added the shortcut, click "OK" to close the dialog, and, making sure you've selected your custom Keyboard setup, click "OK" to close the Preferences. Your keyboard shortcut (Ctrl+Shift+D in the example) should now duplicate the current tab.
If you want a mouse gesture rather than a keyboard shortcut, it's quite similar - duplicate and edit your custom mouse setup to add a new gesture and set "Duplicate page" as the action to have the mouse gesture clone your tab.