I read that the source of Karst topography is coral reefs, when coral reefs are found in water bodies, how is karst topography formed on land?
Karst topography on land is characterized by sinkholes, springs, losing streams, and caves. They are formed by the dissolution of easily dissolved carbonate rock such as limestone and dolomite. The rock is dissolved by carbonic acid in rain.
The carbonic acid that causes karstic features is formed as rain passes through the atmosphere picking up carbon dioxide (CO2), which dissolves in the water. Once the rain reaches the ground, it may pass through soil that can provide much more CO2 to form a weak carbonic acid solution, which dissolves calcium carbonate.
Here is an illustration of karst topography:
Here is an illustration of karst formation: