Where 'target_id' of field_data_field... tables points?
If you look in the field_data_field_{field_name} table, you will see these columns:


entity_type: tells which type of object the target is.
entity_id: which one in the entity table


For entityforms, you can go to the URL /admin/structure/entityform_types/manage/{entity_type}/fields, and you can see what the {field_name} refers to by finding {name} in the list.

So if you know what type of object it is, hopefully you know how to find the list of fields.

If not, go to /admin/reports/fields and search the full list for your field.