when to use ya ni panimayo and ya ni znayo ?

Question

when to use  ya ni panimayo  and  ya ni znayo  ?

Answer

Я не понимаю. =I don't understand. Я не знаю.= I don't know.

Answer

I will just correct the pronunciation:

Ya ni panimayu. Я не понимаю.
You can say that, when you don't  know the meaning of what someone is telling you, or the language that they speak 
e.g I don't understand Chinese. Я не понимаю китайский язык.
I'm sorry, I don't understand you. Can you explain that again?

Ya ni znayu. Я не знаю.
You say that :
1)when you don't have information about smth,
e.g.I don't know the right answer. Я не знаю правильный ответ.
2) when you aren't sure about smth
e.g. What are you going to do this evening?-I don't know yet. Я ещё не знаю.(because you haven't made  your mind up yet )
3) when you aren't familiar with a person, place etc: 
e.g. I don't know him. Я не знаю его.

Answer

Natalya is right. For example - you can know, but don't understand. Like rules of grammar) or - "я понимаю твои чувства, но не знаю, что их вызвало". I understand your feelings (I see that you are happy, sad etc - but I don't know what coused it.