I don't think there is a direct bus that goes from Waterford to Cork airport. You would have to get a bus to the bus station in Cork city centre, then get the aircoach to the airport. Check out bus eireann for times that this bus goes at.
there is an hourly service from waterford to cork..i dont have the precise times but the bus to the airport from the bus station in parnell place cork leaves at 10am 10.25 10.55 11.20. hope this is of some help