The 'finding out' part is easy, but the confusing part is what you're supposed to call the person who just changed their name.Hm... If I started calling you One Piece
I wonder when my hair will dry.
But I really want to, just for the sake of confusing people I wonder why MK ever bothers to change from Meitantei Kiddo to Meitantei Kaitou Kid and back again.