A proof would have much deeper mirrors, sharp, squared off edges, and frosty ("cameo" or "deep cameo") devices. Here's an illustration (using 1971 nickels) which someone posted on another forum. Image source This next photo shows cents, but gives you a better idea of the difference in appearance between a regular business strike coin and a proof. Once you're used to the difference, particularly after comparing them in hand, you'll find a proof coin usually sticks out like a sore thumb. They're really quite impressive looking. Image source
@CDW i highly recommend purchasing The Guidebook of United States Coins. It's filled with a tremendous amount of information. It will be the best $12-15 you'll spend on the hobby
Your 2000-D coin is not a proof, HOWEVER, a decent number of 2000 nickels were struck "prooflike", with fairly clean semi-mirror-like fields. Yours looks like it started as one of those and has seen some wear.
Yea the back doesn’t look as good as the front. I kept thinking man this thing is way to pritty not to be a proof obviouslybit is not but I think you hit the nail on the head.
I just checked the NGC population. NGC has certified 6 2000-D nickels as MS6PL. Six steps AND PL. One at 65, three at 66, and two at 67. I don't have a ready source for PCGS pops here.