How do you attach playing cards to bike spokes to make noise?

You don't. You fold part of the card double around one of the struts to the fender and secure with a clothes peg, with the other end of the card protruding into the spokes. You can also run a string from the outside end of the clothes peg and up th the handle bar. That allows the rider to manipulate the angle of the card against the spokes and create different sounds