Hey!
In the group exercises that I have completed previously at ACs, I've found that they usually focus more on commercial awareness rather than being legal-focused. For example, things such as client pitches to win work for the firm, delivering a presentation to a client / supervisor on recent trends in a specific industry, a negotiation for a draft contract, etc.
I'm sure it differs between firms, but I'd say generally, group exercises will usually involve being given a commercial scenario (in some format) and then having to reach a conclusion as a group based on all of the factors / risks / opportunities. It's less likely that they'll be asking complex legal questions - particularly as the exercises need to be accessible to non-law students.
I'm sure others on the forum might be able to give some other examples too, but those are mainly what I have experienced. As long as your commercial awareness is up to date and you understand the factors and trends impacting the firms' main client industries, I'd say that should be more than enough. Best of luck!!