Taping any of the meta keys (Ctrl and Alt) in this case, will combine
with other keys to send the appropriate keys.
If you want to produce a "Ctrl-C", tap the "Ctrl" on the bar in the
console or on the key widget in the VNC app. In either place they'll
remain highlighted until you tap another non-meta key, like "C". At
that point they'll send a combined key like "Ctrl-C" or whatever key
that was pressed.
Dean