All you'll be able to tell is if the features are correct for it to possibly be German. But most central European gear will look German, so it'll be difficult to tell.
Notable features:
Yokes, back and/or front
Shoulder padding bulky and squared off
Interior pockets - fabric extends from front facings into the liner area. Pocket is cut into this fabric extension, rather than into the liner as a British overcoat would. And pockets are set high up towards the armhole.
Not quite so distinctive but check the style of stitching in the back of the collar. Zig-zag up and down, or side to side?