Well, as a matter of fact, jack nicholson is one of the most famous actors in the United States and an Acadamy Award nominee for his outstanding acting skills. Anyway, the type of sunglasses he often wears, since he wears lots of types of sunglasses, is called aviator sunglasses. I think that kind of sunglasses are quite awesome, you can find those sunglasses at some large optical stores, maybe Alibaba and eBay are also preferable.
Actually, jack nicholson has worn many different kinds of sunglasses, Ray Ban sunglasses is often worn by him. He always wear Persol, Serengeti or Clubmaster sunglasses, which are a discounted Ray Ban variant from the mid-1980s to the early 1990s. You can find them in Ray Ban exclusive shop, but I recommend you to go shopping online.
The type of sunglasses jack nicholson wears is so cool at the appearance and excellent at the quality. If you want to buy one, you could go to the amazon to have a search. There are many types of goods with creative designs, including many hot goods that many stars wear. Thus, there exists the great opportunity for you to get the type of sunglasses jack Nicholson wears.