If you copy a list this will create a new list linked to the same DB table.
If you want create a new list with a new DB table but with an existing list/form/elements structure use the "content type":
Go to the form listing
Click "Export" on the form you want to "duplicate"
This will create a file form-name.xml with the structure of your list/form (groups, elements, validations...) stored in your-site/administrator/components/com_fabrik/models/content_types
Create a new list, set label and table name, Save
Select the content type you just have created, Save+Close