As an event organizer, you have the ability to display what your license holders can or cannot see when they scan a lead. Under the "Registration Form", there is a column titled "Lead Retrieval", where you can mark each field as "hidden" or "visible". This is also the case for custom questions. If a field is "visible" lead retrieval users will see this field whether the lead does or does not have a response to that field.
See screenshot below: