I have a "Citypass." Do I have to make a reservation OR wait in line?

Check your pass terms and conditions. I dont believe One World Observatory is included in CityPass.

I 'm not sure that citypass work for the one. In doubt, make réservation.

No reservations required with city pass and you are moved to a separate window so there is no waiting to speak of?

Unless you have a priority pass, you would need to get in the line at the gate.