During MMIs and group interviews, you will need to demonstrate your collaborative abilities. Ask questions based on your interactions and observations of others. Try not to be hostile towards your fellow applicants.
Also, for some MMIs, you will be doing activities or answering prompts alone. You can formulate questions based on your thoughts regarding these prompts and exercises. Keep in mind MMIs are short and strictly timed. You may not have the opportunity to ask questions in this interview structure.