πότερα δὴ seems clearly right (see cr. n.): the “δή” gives indignant emphasis. δὲ is also possible (cp. 917); but it is weaker, and gives a less good rhythm. For πότερα in a simple question (like Lat. an), cp. O. C. 333. κερτομῶν, of bitter jest; cp. Ant. 956 n.