In the first little "plaza" of Colossus Boulevard, you should see a little path leading down to a building. Go on inside, and there's a spell trainer named Mildred Farseer (iirc) who will teach you reshuffle as long as you're level 20 and have a training point.

What is reshuffle wizard101?

Reshuffle is only supposed to restore the cards you discarded.

Where is the reshuffle treasure card?

You can buy them in the Wizard City and Krokotopia libraries.