So I have a male Greninja with Protean and a female Frogadier with Torrent. What are the chances that my Froakies get Protean?
In your case you need a female Froakie/ Frogadier/ Greninja with Protean, and a male of the same egg group. The male doesn't matter in this case and can be any species as long as he's in the same egg group.
Male Pokemon have a 20% chance of passing down their hidden ability only when breeding with a Ditto.
Bulbapedia - inheriting abilities