No, jonin medal does NOT give unlimited rich field attempts...

The easiest way to tell if you have the medal is see what is your maximal stamina amount.

Edit: Just FYI, the no cooldown for richfield thing no longer does anything. Before 3.0, however, there was a 10 minute cooldown before the two attempt of richfield for non-medal players. That's what it's referring to, a deprecated feature.

I don't quite remember, but I don't think you see your own medal when you do that....

Thou someone else can inform you of the fact if you don't.