The only thing I can offer with the limited amount of training I've had, don't go for a kill with a normal knife. Go for the ligaments connecting major joints. Wrists, elbows, and knees. If the knife has a decent geometry and sufficient force can be applied then maybe a larynx strike may work. If you have some kind of length and an angle then stab repeatedly into the taint area, like if the guy has you mounted and your arm trapped underneath. Maybe you'll catch one of the arteries. Go for the eyes or just behind and below the ear canal if presented.
Having said all that, if I was carrying a pocket knife solely for self defense I'd carry the civilian or something like the matriarch or harpy. But that's because I'm pretty untrained in real life, have only been stabbed once and shot at a couple of times and have only done a little Kali, Krav Maga, and more extensive wrestling, boxing, and BJJ mixed with law enforcement training which focuses on the normal stuff like pistols, rifles, batons, OC, and tasers. The reality is everytime it came when it wasn't expected and by the grace of God I'm still here. It really does come down to familiarity with your tools and the human anatomy mixed with some ingrained muscle memory targeting the simplest and most effective targets. The heart, head, liver, etc are doable but the elbows and wrists will most likely be the closest and most undefended targets and the hips (and all the ligaments, tendons, and arteries contained) are the least mobile.
The head is the CPU, the hips are the gearbox with a lot of the hydraulic hoses running very tightly together, and the joints are the wheels. Gotta immobilize the threat via one of those. A knife just cannot penetrate or smash the CPU or gearbox so use the knife for what you can and cut the hoses where they're all bundled up or slash the tires. You can't throw a tourniquet on a gushing artery in the hips, either.
Just my thoughts. Having said that train with and carry a pistol if you can. Any pistol is more effective than knife. And train with your hands and feet. At least then you might have a chance to effectively block and run/counterattack if needed before you ever have a chance to consciously react.
And having said all that I'd defer to a guy like Mike Janich any day of the week and into the next.
