What, when. What and when are often used as exclamations of impatience:
“When, Lucius, when?” Ib. 5. Some ellipsis is to be supplied, "What (is the matter)?" "When (are you coming)?" So in
“What, Lucius, ho!
See also What, 253.
“Gaunt. Throw down, my son, the duke of Norfolk's gage.
K. Rich. And, Norfolk, throw down his.
Gaunt. When, Harry, when?