In a sugar such as a disaccharide are both ends of the sugar known as reducing ends?
No, in dissacharides the reducing end is situated only on one monosaccharide which is having free anomeric carbon. This carbon does not take part in glycosidic bond formation and can form open chain. 





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https://chem.libretexts.org/Courses/Sacramento_City_College/SCC%3A_Chem_309_-_General%2C_Organic_and_Biochemistry_(Bennett)/Text/14%3A_Carbohydrates/14.6%3A_Disaccharides