STOP -- DON'T DO IT.
Wherever you heard about this (movies, TV or the Interweb) it's a colossally bad idea.
In a survival situation, a knife can be one of your most valuable tools. And if you're fortunate enough to have a knife in your possession at a time like that, the last thing you want to do is tie it to a stick and throw it around. You'll either break the blade (and render it useless) or you'll lose the knife completely.
Sure, your knife may have hollow pins or even an exposed "skeletonized" tang, but please, we're begging you, don't try to turn it into a spearhead.
If you still want to practice spearing fish or other game -- which can be a useful primitive skill -- you should learn how to make a proper spear by sharpening a pole and fire-hardening the point.