well maybe we need to ask what quality is lost going from wave to flac level 6
None at all - that's the whole point of lossless compression, the original data is recreated 100% upon decompression, it is just stored in a more efficient format.
so we can understand what frequency range is lost going from flac level 6 to mp3 320kbps.
It's not a simple matter of a particular frequency range being lost. What information gets lost is very much a function of the original source material and the particular encoder used. 320 kbps mp3 is not a sufficient description to know exactly what encoding steps were performed, different encoders make different "choices" about what information is ok to lose, after first stripping out "redundant" information that can be recreated perfectly by the decoder.
comparing two of the same audio files is probably nearly impossible for most people but what about comparing a raw photograph (as in the format, raw) to a very, very high quality jpeg. would we be able to distinguish the difference?
As you are probably aware, jpeg is a lossy compression scheme (like mp3). An analogy to flac would be making a zip file of the raw image - the information is 100% preserved. Beyond that I'm not sure how the comparison is relevant - a highly compressed mp3 is obviously audibly inferior to the original wav file, while a higher bit rate mp3 made with a better encoder may be audibly indistinguishable. But analyzing it on a bit for bit level you'll be able to detect a difference, just like a pixel for pixel comparison of a raw and jpeg image. There's no reason to expect a certain % reduction in file size via jpeg compression and the same % reduction via mp3 compression to have the same impact on how close the compressed file comes to reproducing the original, the compression algortithms and the information needing to be preserved are just too different.