This gathers a number of people to work on a specific task or to discuss a particular topic. You'll be observed by recruiters. To help you prepare, think about the role you naturally tend to play in a group situation. What are your strengths? What are your weaknesses?
If you are usually a leader, remember that this is a group exercise. If you are a person who tends to hold back and listen, remember that your voice must also be heard.
If it helps, get some feedback about your behaviour and tactics from someone who has already had the opportunity to work with you. On the day of the group exercise, get fully involved. Stay calm and focus on your performance, but listen to what others say. Try not to be influenced or annoyed by the behavior of individuals in the group. Be yourself.