might I have a cookie please? very proper may I have a cookie? propper could I have a cookie? common usage

the second one is good.Learning here.

Look for the following examples they may help you to understand them : I might go to the cinema tonight. I may go to the cinema tonight. I could go to the cinema tonight. And all of them are for possibility. If you have a particular point to ask about if you haven't got your answer yet.