Well, a good Don Sphynx is rubber naked, different earset, a bit muscular then the Sphynx which is supposed to be "cobby".
The Don itself is from Russia, another difference
The following picture gives a bit of an idea what the differences are. The features are exaggerated, but it I've found it helpfull
From left to right you have the Peterbald, Don Sphyxn and Sphynx