Just my 2 cents for the folks who might be interested medically.
You would call yourself left or right handed depending on what hand you use the knife not the pen or mouse or anything else,just knife.
The reason behind it is that you instinctively grasp the knife that is potentially lethal with your dominant hand.
So if you write with your right hand but you take the knife in your left , then you are lefty.
Another fact:
Although the majority of people are right handed right shouldered but People can be right handed left shouldered. Meaning they take the knife with their right hand but the gun to their left shoulder. My father was one of those guys . He was 100 right handed like most of us but took the gun to his left shoulder.
Did it worth 2 cents?