why couldint josnie see that frankie Wasa perevert why wouidint she listen to Howard marion and chachie

Because that's the way it was scripted. ;)

because Joanie was naive and trying to prove that she was competent and mature enough to do the job.

what Happendto frankie agter that does anyone know?

Fonzie caught him in a dark alley and "took care" of him. :-D