Translation:I do not know what you are going to ask.
How would you translate "I do not know that you are going to ask" (that instead of what)?
"Eu não sei que você vai perguntar". If you hint word for word you'll find o=the, que=that. But, if you find "o que", the translation is what
I think it's only quê at the end of a sentence, to show a difference in pronunciation. In the middle of a sentence it's pronounced "kee", at the end of a sentence it's pronounced "kay".