I wouldn't even know how to practice knife-fighting. How does one train for that?
The basics are grip, stance, blocking and striking. The first three are very similar to any basic martial art. Striking with a knife needs to focus on the fundamentals - stabbing and slashing.
Stabbing needs to train to turn the blade horizontally so to allow he blade to slip between the ribs and not get stuck. Hitting the vital areas is important - heart, liver, lower lungs, throat. Never stab at the head. It is possible to bleed out before the ambulance arrives so stopping bleeding is very important post fight.
Slashing is designed to leave long gashes and to sever veins , arteries and tendons. Target areas include wrist, inside elbow, underarm, neck, lower abdomen, inside upper thigh, and rarely back of knee.
All attacks can be trained on a dummy with a practice knife. Do not practice any of the fancy knife tossing and switching hands or grips. Basic pokey pokey slash slash will do you a lot more good in a real fight.
Understand that the WILL BE lots of blood. If they have a knife, you are also HIGHLY likely to get hurt as well. So it is also very important to know how to administer first aid to yourself and others if needed.
Big magic markers. The marks are the “cuts.” Obviously, use clothing you don’t mind getting stained.
Most uses of knives are more like surprise attacks or using a knife on someone who is unarmed.
Probably the first rule of effective uses of a knife is to keep it hidden. If you are up against someone with superior weaponry, strength or size, if deadly force is justified, do not give a hint that you have the knife until you employ it, rapidly, ferociously and repeatedly.
I gave my daughter a knife, and said if she ever had to use it, use it fast and hard against effective targets to disable your attacker; once you get free, flee so that they cannot grab you.
There are numerous books and videos on knife fighting. My favorite is “Knives, Knife Fighting, & Related Hassles How to Survive a Real Knife Fight” by Marc “Animal” MacYoung
If you decide to show the knife, (deterrence is more likely than any other reason) learn one or more fighting stances. Keep the knife back near your body so that it cannot be easily kicked or knocked away. The other hand should be used to protect the knife hand.
At least you want to *look* like you know what you are doing.
http://www.pabujinkanbarndojo.com/equipment/index.asp
I spent years working with knives, you need friends that will practice with you, the kind of thing that a lot of physical 20 year olds do constantly, fight, fight, fight.
If your friends during your 20s and early 30s are not the type who love to fight and wrestle and play rough constantly, then you probably need to join a class or something.
Don't practice “knife fighting” that instills a duelling mentality. You do not want to get into blender contest ala’ Tommy Lee Jone/Steven Seagal. A more accurate term would be knife killing. A human can remain conscious and dangerous even when a major vessel is cut.
Look up The Dead Mans 10(seconds). You want as close to a one hit stop as you can get.
Google Darren Laur - Gladiator School. Straight from the prison system based on practical experience. Surprise and a straight deep horizontal thrust through the armpit will reach a lung,collapsing it, and the recipient will buckle allowing follow up as needed or run like hell.