code: def show_field_mapping(self):
          
          from safe.gui.tools.field_mapping_dialog import FieldMappingDialog
          dialog = FieldMappingDialog(
              parent=self.iface.mainWindow(),
              iface=self.iface,)
          if dialog.exec_():  # modal
              LOGGER.debug('Show field mapping accepted')
              self.dock_widget.layer_changed(self.iface.activeLayer())
          else:
              LOGGER.debug('Show field mapping not accepted')
docs: Show InaSAFE Field Mapping.