Most common ones I came across over 10+ co-op interviews:
What projects have you worked on?
Have you worked in a team? If so, what was your role in it?
Have you ever had to deal with problems caused by a team member? How did you handle it?
Why do you want to work for us?
What do you know about our firm?
Tell us/me about yourself?
For a more comprehensive list of questions, visit the following link by ECCS McMaster:
http://www.eng.mcmaster.ca/eccs/documents/interq.html