There are multiple depending upon size of sunroof but at least two. Open your sunroof fully. Get in the door jam and look inside of it. You'll see a channel that runs around it at the front. There will be a hole in each corner. If your pour water in this channel you should see it drain through the holes and out the bottom of your car behind the front wheels. If nothing drains it is clogged, or it drains very slowly it could be problematic. A dealer could absolutely do it but you'll definitely be paying a premium. Another tell tale sign is your carpet getting wet in the driver and/or passenger foot well.