If you are logged in with the correct account then it should appear in the Purchased tab in the App Store app. But re-download content from an account will potentially tie the iPod to that account for 90 days : http://support.apple.com/kb/HT4627
As an alternative you could copy it from your iPad to your computer's iTunes via File > Transfer Purchases (File > Devices > Transfer Purchases on iTunes 11) and then sync it to your iPod
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