番薯 is sweet potato, and 糖水 is sweet soup (糖 is sugar or candy, and 水 is water), so 番薯糖水 is sweet potato sugar water.
About This Dish
Sweet potato soup is a sweet soup made from sweet potato boiled with rock candy and ginger (a sweet sweet potato soup!), cooled and served as a dessert at the end of meals.
Trivia
There is a character in Old Master Q named 大番薯 (Big Potato).