The chocolate, peanut butter, and any other ingredients that could be genetically modified most likely are. While delicious, there is not many natural - let alone organic - ingredients in Reese's Peanut Butter Cups.
Honestly if you truly cared about GMO's you would not be eating Reesie's. They're more than likely completely Full of GMO, and honestly people who consume them are okay with that. Even though they shouldn't be. Just so tasty
If you're trying to avoid GMOs, you should avoid buying anything made by Hershey or Mars. Unfortunately, they're not going to publicly release information about how many GMOs are in each product, so we can't find out the answer for that.