What I have to return from mainReadQuotes?

I am confused about returning data?
Do I have to return symbol names by sorting closing price for all dates?
or
Do I have to return symbol names by sorting closing price for only end date?
or
Do I have to return all details about specific stock at specific date (for all dates)?

you have to return symbol names by sorting closing price for enddate (your 2nd option)
(but don’t forget to consider that given enddate may not be present in the data)