Add event fields
Just like you can create data fields to forms in YoungCRM, you can create event fields for the Event Manager.
You'll find event fields in your organisation settings.
When creating your event form, this can be created by both person cards and event fields. Therefore, you can simply use person cards to create your event field, granted they have sufficient information about the people who sign up for the event. If not, it's necessary to create some customized fields for the event.
Here, you could ask if they've participated in an event before; ask where they've heard about the event; or why they want to participate. These are questions it would make sense asking in relation with events.