On page 21 of the Rulebook.

You may turn in as many Monsters as you wish at one time. You gain one shtick draw for every 3 x symbols.

I assume that means you draw three shticks, choose one, put the other two on the bottom of your shtick deck, then draw the top three shticks on the deck after putting the other two on the bottom... choose one of the new three, and put the other two under the first "other two"... continue doing so.

I'm assuming you were asking if you could choose 2 or even all of the three cards drawn when you trade in monsters...

And of course... maybe I shouldn't even be replying, as I've only read the rules (over and over and over and over... and over) and not played the game yet.