If you are logged in with the same account that you bought it with then it should show in the Purchased tab in the App Store app on your new iPad for downloading on it. If you've moved countries since buying it then it won't show in Purchased (and will show the price in the main part of the store), but if you try to redownload it from the store you might not be charged (as long as it's the same app and the same account) - I haven't moved countries (so can't confirm) but people have posted that if they've already bought an app that they get a prompt for whether they'd like to redownload it for free when tapping on the price.
Or do you have it in your computer's iTunes library, or still have your old iPad with it on ? If you still have your old iPad with it on then you could connect it to your computer's iTunes and do File > Devices > Transfer Purchases to copy it over to your computer so that you can sync it to your new iPad.