What have you done since this morning? As far as I know, there is really no standard reply to this question. There might be depending on the particular relationship between the two individuals. For example, if your boss asked you this, a standard reply might be "I've been working really hard since this morning, do you want to see?" (meaning, can I show you the evidence of the progress I have made since this morning). If your spouse expected you to complete a list of "chores", the answer might be "I have been working through the list and a lot has been done.". However, generally speaking, if a friend, co-worker or family member asked the question, you should just tell them whatever it is you have been doing. It is a general question that is simply meant to start a conversation.

I think that depends what you really did and who asking.

This question is gramatically wrong.Since should be used with present perfect not simple past

if an Interviewer ask this question to me then what'd be the standard reply.?????????/