The knife is actually my prefered method of self defense. I'm by no means a master, but I can offer a few suggestion.
First, you need to understand what a knife can do offensively. It does not take a knife expert to be dangerous with a knife, as the tool itself is deadly. It cuts whatever fleshy surface that it touches. That means, if it so much as grazes you, you bleed. Do your research on knife wounds before you even consider facing someone that you KNOW is going to be armed with a blade. Trying for the disarm is somewhat foolish. Even if you have an idea of what youre doing, there are too many things that can go wrong. Trying to control a knife while it's in motion is nearly impossible at combat speed. You will be cut or stabbed, period. Even if you have a knife of your own, blade to blade combat is the stuff of Hollywood. On or both combatants would die in real life. To combat a knife, you need a superior weapon, one that offers you some distance. Want that blade as far away from your body as possible. Some quick tips if someone pulls a blade on you:
1) Run away.
2) Look for a weapon of your own.
3) Defend by using a chair, try to entangle the blade with a jacket, take off your belt and swing the buckle, always your mind should be on escape.
If all else fails, DO NOT allow yourself to be cut or stabbed in any vital areas. Don't try to grapple with a knife fighter. Don't go for complex joint locks, and for God's sake, DON'T TRY TO FIGHT HIM ON THE GROUND. That's suicide. Use the outside of your forearms to block, try to keep him at kicking distance, and keep the kicks low. Your best chance for the escape is disabling his knee. Remember ESCAPE first. A knife disarm is the last resort. If you have to grab the knife, use both hands on his knife hand, and either try to redirect the blade towards him, or try to get to a position that is better for you tactically.
If your father is smart, he won't help you train in knife disarming. He'll probably only teach you enough to get you killed. Oh, and stop playing with knives. Like any weapon, it should only be carried by someone RESPONSIBLE enough to have one. One wrong move with any kind of weapon can ruin your life, and end someone elses.
Blackbelt in TKD/Hapkido. Weapons and self defense training aquired in a long career in private security, advocate and enthusiast of self defense training.