As my users have a conversation with my assistant, there is no easy way for me to see when there are no results returned from Document Search or QnA.
QnA does have a 'misses' area, but for me to know there are misses I need to go in there, there is nothing in the Dashboard (or similar) telling me there are things I need to do.
There is also nothing for misses with Document Search.
My aim is to close the conversation loop, so if my assistant is being asked a question it can't answer, I need to know so that I can review that question, determine if it's a sensible question, and if so, add the answer either through QnA or Document Search, depending upon what data source is being queried.
I could add Expert Assist into the mix, but I am intending to supplement QnA / Document Search as it is needed to fill those gaps within its knowledge if it's a question I can answer.