Alright. My very first thought and advice is DO NOT DO IT! Getting into a fight with another person and both yourself and your opponent are armed with knives is tremendously dangerous. To face off against someone with a knife and you are unarmed is flat out insane.
I have trained with knives before however the stick is my specialty. What I will say is that should you face off against an opponant and both of you have a knife – you have a 1 in 3 chance of surviving. Not very good. How?
If you are trained to use a knife and you opponant is not – you will win.
If both of you are trained and are of equal skill – you will both die.
If your opponent is more skilled than you – you will die.
Pretty simple huh?
Regardless – if I were to find myself in a situation where there is a potential violent confrontation and the other person has a knife – I will retreat if at all possible. In fact even if they do not have a knife my philosophy is to avoid physical confrontation at all costs.