So, a little more in this and all of this is a bit speculative. Geo's observation that Wittgenstein was flying with 9/NJG2 on that night seems correct and on that basis, the aircraft code would have been R4+_T where the underscored letter would have featured the yellow squadron colour. On that basis, I found the below picture from
Fly Boys which is purported to be "Heinrich Prinz Zu Sayn-Wittgenstein and his crew from 9/NJG2pose with their Ju 88 C-6 R4+ET, marked with 21 victories on the fin, during the autumn of 1942. "
Whether or not this was the same plane that he flew in July is unknown to me and I've not been able to find any pictures or profiles of his mount in this timeframe. (All of the profiles I posted above in Post #2 are of his later machines). George may be able to confirm this but your uncle's aircraft might have been Wittgenstein's 13 or 14th victim as, according to the Wiki link George posted above, he scored victories 15 thru 17 on the last night of July/42.
So, assuming that the picture above is the same aircraft, my suggestion for a scheme would be standard 70/71 splinter scheme on the upper surfaces (you can see the demarcations of the colours in the above pic on the fin and horizontal stab), appropriate number of victory tallies on the tail, black undersides, black letters with the 'E" outlined in yellow and the standard NJG 2 emblem on the nose.
Again, all this is a bit of a reach but the best I can do. Hopefully someone else has better info.