歡迎 (Huan Yin).
sup- ba' The previous answer was in Mandarin (Putonghua).
hongi kongi
There are two ways to say thank you in Cantonese the predominant language of Hong Kong. You can say 唔該. M̀h'gōi (Mm Goy) when someone helps you and 多謝 Dōjeh (Doe Jay) when someone gives...
Most people in Hong Kong merely say "bye-bye", although in proper Cantonese it should be "再見" (pronounced joi-gin).