Typically Echinaceas blooms (and zinnia blooms) have both male flower parts (pollen florets) and female flower parts (stigmas). You can pretty much pick any plant to be a female plant. But a male plant has to be one that is producing pollen.
In zinnias, I usually pick the female plants as the ones which aren't producing much, if any, pollen. That way I don't have to spend a lot of time emasculating them (removing the pollen florets). I am attaching a picture of one of my echinacea flowered zinnias from last year. I get these by crossing scabiosa flowered zinnias with long-petalled zinnias.