First fields are not defined in layouts, they are defined tables. Layout names and table occurrence names often match, but they can often be different also. having 20 different tables, each with 10 container fields sounds like a database design that needs improvement.
While some script steps have an indirect reference version where you can calculate the name of the field, Export field contents is not one of them. You can, however, use go to field or go to object to put the focus in a particular container field and then use Export Field contents without specifying any specific field and then this step exports the contents of the field with the current focus.
But I think you need to re-evaluate the underlying design of your database.