If by cook knife you mean chefs knife, this is the most versatile knife in the kitchen and you will use it for most of your cutting in the kitchen so it is a good investment. Paring and specialty knives like butcher knives, scimitars, etc would be the other, much less used knives.
I helped with a local cooking school for a few years and our best chef, who was also the head of the community college culinary department taught our knife skills class. He said the knife he reached for the most was a 10" chefs knife and he had several of his personal knives he'd bring to our classes.
At that time I was using my 6" chefs and 8" chefs knives the most but have found myself preferring my 10" chefs knives the most now. The 10" is the most versatile as I can use it for larger things easily like cabbages or other bulky vegetables that are harder to cut with the smaller knives. So...if someone were to ask me what I thought would be the best knife to spend a whole lotta money one, I'd say the 10", based on my experience. And Shuns are excellent, in fact, one of my teachers favorites was his Shun.