First, set your field appropriately as Individual, Group or Both. Then for group registrations, fields have the ability to be set as "Each Member", "Billing Only" or "Members & Billing". The tooltips explain further and the video tutorials go into even more detail... but if you don't see a field, it's because you haven't enabled it for the type of registration you are doing.
Make sure the default settings of the field are as desired... and also that the field settings within the event are as desired.