From Tseung Kwan O to Hong Kong Airport. Flight at 9.05 am.

I have two ways for you:
1. By MTR: the route is Tseung Kwan O Line - Island Line - Airport Express Line
The first train leaves at 6:04 and takes no more than 70min to HKIA. Theoretically, this way will do. But if it take some time to transfer on the way, ur time will be pressed.
2. By bus: take bus no. A29P at Tseung Kwan O Station and it takes 70-75min to HKIA. The first bus leaves at 05:40, so you can catch your flight. Personally, this method is more recommended.