From the Dona Refuge you take the path n. 577 to the end of the Val di Dona, then go up the scree that runs along the Sasso di Dona on the path n. 580, which leads to the Dona pass (mt.2516).
From here you can reach in 15 minutes the Antermoia Refuge (mt.2497), and from the Refuge continue for a few minutes until you reach the lake of Antermoia.