This is probably really simple but can someone tell me how to get the psynergy..

In Osenia, south of Alhafra and the Yampi desert, there is a town called Garoh, and west of that, there is a town called Mikasalla... In a desert north of Garoh, there is a rock called 'Air's Rock' and that is where you receive Psynergy 'Reveal'

Usually when you play the game you end up going to these places first... But it's possible to miss these places entirely, due to the slightly non-linear nature of the game... (it's up to you to explore the continents...)

I prefer to actually play the way you have done, because otherwise, you end up tackling Air's Rock with only three in your party, and at much lower levels... You may have noticed, Piers' level is much higher than Jenna, Felix and Sheba's... So If you want all the levels to match up early on (they will normalise later on in the game as you play anyway....) then you should do Garoh, Mikasalla and Air's rock before freeing Piers. But your way is better...

You can get to Air's rock either by going into Yampi desert from Alhafra, and going to the place where there is a sign saying something like 'warning! No return if you go down here' and a sand-fall... Just go down the sand fall and head south once you leave the desert. Or you could go to mikasalla and Garoh the other way, when you first cross over the bridge near Madra into Osenia, head south past the Yampi desert entrance, but don't go in... Keep heading south, and then head east... You may find Mikasalla around here... There's a djinni there... Read the minds of the farm animals behind the house. Then leave Mikasalla, and head east... You will eventually come to Garoh... Go in... It's night, and there is a full moon... Aw-aw-awoooooh! Then head norht to air's rock. If you have just gotten piers' boat the second way might be the easier way.

So go to air's rock, and find reveal! It's a pretty big puzzle place so it will keep you occupied... Have fun!