Gigi, but if you want something more suttle go with Ava.
Giovanna Federico goes by Gigi.
Giovanna Fletcher goes by Gi.
Giovanna Kline goes by Genna.
Giovanna Cappetta goes by Gigi Cappetta.
Giovanna Acha Aleman goes by Giovanna Acha de Chacon.
Giovanna Maltese Eibl goes by Gio.
Maria Giovanna Elmi goes by Fatina.
Rozzii
Some cute nicknames for Juan could be Juju, J-Boy, or Jay.
Giuseppe Sanna goes by Beppe.
Audge Auds?
Johnny Boy !