Will it be easy to take a taxi from Disneyland resort to NOVOTEL Citygate hotel at around 9pm?

Well, I'm afraid it will be a little hard to hail a cab at that time, bcause there will be many people waiting for cabs.

If you really fail to have one. Don't worry! Take Disneyland Resort Line to Sunny Bay Station. Then transfer to Tung Chung Line to Tung Chung Station, Exit C. The whole way takes around 25 mins with the ticket fare of 13.9 HKD per person. After arriving, walk northeast around 150 yards to find your hotel.