This alluring corner hideaway is on Williamsburg’s south side, where expensive cocktail bars have replaced the dwindling Puerto Rican neighborhood’s once ubiquitous bodegas, barbershops, and social clubs. So it’s fitting, if somewhat tragic, that the clientele drinking Donna’s signature cocktail, a rum-heavy spin on the piA a colada, are more likely to associate it with spring break than with its status as the national drink of America’s largest territory.