Howdy,
Is it possible for play an upper octave G# on a D chanter?
If so, how is it fingered?
Many thanks,
A.C.
With a G# key. 
It would be very difficult to half-hole (with the third finger).
O’Farrell gives a fingering for G# (same for both octaves), but it doesn’t work very well on any of my chanters:
X
_
X
X
O
X
X
X
O
It works better in the second octave, but pretty much only in an A-G#-A situation, and you would have to practice the crap out of it. Ronan Browne used it in the Morning Thrush if I remember rightly. If you need a descending G# you need a key. In fact just get a key.
Many thanks for the suggestion, but with my present practice set, the fingering does not give me anything other than a subtle change in timbre.
I’ll experiment further when I take delivery of my full set in October.
All the best,
A.C.