Recipe calls for 3/4 cup of cider
That would make for a very tart/sour recipe. What are you making?
It depends on what you are making, but generally no. Vinegar and cider are two very different products. You could probably substitute apple juice though (and lower the sugar content of the recipe).
There is no added sugar in apple cider or apple juice. Are you thinking of hard cider? There is sugar added during fermentation as food for the yeast, similar to kombucha.
no but simply apple juice has a great cider flavor if you can't find the local stuff
Center cut pork chops
As much as you could substitute wine vinegar for wine really not. Some cider vinegar (offset by something sweet- I use maple syrup) would be good with your chops, but it's much too acidic for a primary braising fluid- try white wine, with maybe 2Tb. vinegar/ cup of liquid.