I have no formal training in knife throwing, but it is a personal hobby. What seems to work for me in a throwing knife is weight. the heavier the better.
That and learning the weight distribution of the overall weapon. It seems just about any knife will do as long as it is not so light that an air current could alter the flight.
I recently purchased three that have adjustable weight along the back.
For a good quality thrower check out SKS bayonets. They are durable, nearly unbreakable and will last a long time with minimal care and occasional resharpening.
I have a host of other thrower blades from Cold Steel , to knock off varieties, Bowies, Balisongs, nails ....
I have a clip up on demonstrating some basic projectile work with the SKS bayonets on www.Bujinkandojo.net check it out when you have a moment.
I throw lots of stuff, edc folders, fixed blades, spikes, stars, ball bearings, objects I'm likely to pick up, etc. I have not tried sks spikes yet but have heard good stuff about them.
What I use like best lately is the Cold Steel Pro Flight 14" thrower. I use it for general throwing practice most of the time.
It's big, heavy and nearly indestructible. I like that it's heavy enough for multi full-rotation throws but still works good for half rotational throws.