Any counter service location where the guests get the drinks themselves they can get refills. This would include all the Resort counter service locations, Earl of Sandwich, Wolfgang Pucks Express, Cookes of Dublin at Downtown Disney, finally the Electric Umbrella and Sunshine Seasons at Epcot.
If the Cast Members are the ones who get the drinks for the guests, then those locations do not give free refills and the guests would have to purchase a brand new drink.