If your examiner asks you for a diminshed 7th arpeggio on C should you play the diminished 7th of C (i.e. starting on B) or start on C?

Likewise, if he or she asks you for the dominant 7th on C, should you start on G (the dominant of C) or C itself?

I can quite cheerfully do either but I wouldn't want to get it wrong!

Dimished 7ths always start ON the note they ask for; dominant 7ths IN the key.
Hope this helped!

I was explaining this to a pupil the other day. The examiner should ask for the 'dominant 7th of C' meaning - start on the G. Some pupils who play guitar might be used to calling it G7, which would mean play G7, so play from G. Strictly speaking the examiner should not ask for the dom 7th using 'guitar speak' for pianists.

Yes - the diminished chords aren't in a particular key so the examiner will just ask for the start note.

My favourite exercises and a good stretch for my small hands