Where do the Notes associated with Gmail accounts get synced to on iPod touch?
There's a difference between syncing with iTunes and over the air sync.

If you set up your Gmail account to use over the air sync then when you open up the Notes app (on the iPod), you should notice a back button on the top left that allows you to change which account you use for notes. If you choose your Gmail account and start creating notes, you will start seeing them appear in your Gmail account, under the "Notes" label. This sync happens automatically once you press the "done" button on each note (as long as you have an internet connection).

This has nothing to do with iTunes sync.

You will only see notes that you create under this account in Gmail. You will not see all of your old notes. For that, see this question.