Hello, Vietnamese passport holder

I am Vietnamese. I will have a trip to Cambodia next week, and I want to get Hongkong visa in Cambodia to travel to Hongkong after visited Cambodia - with my daughter (she is 20 months old). Is it possible? If yes, what documents do I need to prodive to the Embassy and how long will it take to process? I visited Hongkong once in 2013. Thank you so much.