At several moments in this piece there is a top D 3 octaves above middle C (above the highest C you can play). Could anyone tell me what the fingering for this note is? also is it very difficult to play? thanks

Here's a downloadable fingering chart that goes up to the D you are asking about:

http://www.gemeinhardt.com/pdf/fluteFingering.pdf

It's an easy note to play, as long as your name is James Galway Most of the rest of us (ie, the mere mortals), however, will probably have to struggle a bit to get it out.

If I remember correctly there are a few High Ds in the 1st movement in one area. The arpeggio is something like an ascending D augmented triad and climbing to the high D isn't so bad if you work at it slowly at first and increase speed. Now as for Galway, I have a recording of him playing the Ibert Concerto and his last note is the high F above that D. A flashy mod of the original score which does not go quite that high.
These high notes are becoming more common. If you read the text from the Barrere Flutist's Formula and a few other books from earlier in the 20th century, they didn't recommend going that high very much because they believed that it's bad for the embouchure. -Tymes have changed.
~Bilbo

I would suggest looking at www.wfg.woodwind.org for fingerings. There are several that will work for this D, but which is least awkward and speaks in tune and on time will depend on you and your equipment, so don't be afraid to experiment a bit. I recently was reading through some back issues from Flute Talk (going back only a couple years), and I believe one of the articles was specifically about the Prokofieff Sonata. It would be worth reading that if you can get your hands on it. The D is actually not at all difficult to play as long as your flute allows it and you don't have trouble with notes lower than it. To make it really easy, I would suggest learning how to play up to E or F (as Bilbo mentioned, they are becoming more common, so knowing them doesn't hurt), and just popping them every once in a while. You probably won't be called on to perform one of these notes very often, but if you can play above the D, it will speak much more easily for you.