As I have said, Hong Kong is always know as the shopping and food paradise, famous food in other countries will also be available here.
This is pearl milk tea, a bit different from HK style milk tea which is made by Silk Stockings sieve. I think it is not as move as HK style one. But the little black ''pearl'' is really good to try, you can chew and drink at the same time which is a funny eating experience.
You can now find it everywhere on the street for about $8-20HKD. Lately, this kind of Taiwanese beverages shops are all over HK. Well, hopefully when you come visit, they are still along as HK is also famous for following the trend so if the trend of pearl milk tea is out, you couldn't find them easily.