What seemed particularly insightful in the presentation? What would you add?
Which issues require more consideration than what was presented, why?
Were there any controversial issues discussed? Where you do stand on them?
How does your view of a controversial issue relate to where the speaker, author or a classmate stands on this issue?
Once you have selected one of the topics above, you need to do two things:

Connect with what has been said personally – what experiences have you had that give you an interesting perspective on the issues discussed?
Bring ideas into the topic you chose in relation to the media – what do published sources have to say about what was said? What do academics have to say about this topic?