I guess you are looking for something similar to "chotto". In English, there is no such expression. It is perfectly polite to say you are not sure or you don't know. That's the cultural difference. You could make it diplomatic like: I know too little about this area. I lack experience in the field. I am less knowleageable here. I am a novice. I need some guidance ..... I csn say it in a thousand ways :)))))

Hi Emma, Not being sure means you are not 100% certain that your answer is correct. You could be wrong or right, however, I don't know means you have no clue whatsoever. Hope this helps

They can both be used interchangeably. The difference is that "I'm not sure" could mean that the person has some understanding or a guess, but is not certain about it. "I don't know" feels a bit more direct and simply means the person does not know. Saying "I'm not sure" can be used to politely tell someone you don't know :)

'I don't know' means you know nothing at all while 'I am not sure' shows you are not really certain whether what you now is correct.