you just can't
You don't. pokemon saphire was made before wifi existed.
Yup.
yes
in jubilve city
it's not found anywhere on sinnoh you'll have to migrate it from other Pokemon games like ruby and sapphire or emerald, or if you seen them on your pokedex, but haven't captured, use gts using wifi.
You can get it by trade from diamond/pearl/platinum or pal park it from ruby/sapphire/emerald or get it of a wifi event. See related link below to see when you can get him when you can go on mystery gift on your title screen (you will need wifi connection).
because you need better wifi
Via Nintendo Wifi.
In Jublife City
its the card that enables you to use the wifi station in jublife city.
either by cheating or a wifi event (but wifi event expired)
Of course you can. I played my Pokemon Diamond with my cousin that has Pearl.