I think listening is the most important thing you can do. Most teenagers do not want to be "told" anything but they do want and need you to be there to answer any questions, if asked. For some reason when parent divorce, the children sometimes think that it is their own fault or they think that the parents don't love them enough to stay together. Mostly they need reassurance that "they" are not the problem. They need to know that their parent still love them no matter what they may say or do to each other. Sometimes the children are afraid to ask a question. The only question I would ask is, "Is there anything you would like to talk about?"

A good link for this subject: http://www.kidshealth.org/teen/your_mind/families/divorce.html