negation - How to answer a negative question in English?

Q: "Don't you know?"

If I really don't know, how should I respond to this question? Yes or No?

There's a similar question on EL&U, but the answer isn't clear how it works:

Also here on ELU too:

These answers are confusing. I want to know what one word answer I can use. In other words I want to know:

• 
  

  What will native speakers understand if I reply No to this question?

  
  
  


• 
  

  What will native speakers understand if I reply Yes to this question?