You can ask single or multiple choice questions or free text answers if you require specific notes on a lead.
Also, don't just ask the same old "do you want a brochure" or "hot / medium / cold lead" type questions. Think more specifically about your products. If, for example, you're a shoe manufacturer, why not ask specific questions on your products such as: sizes, colours, types.
Think about and set your questions up before the event so you arrive to site ready to start scanning and adding valuable detail to those leads
The possibilities are endless - it's what you make of them.