How do I view my iTunes purchases on iPad?

Where are you seeing the purchase, if on an email it's not a phishing email (http://www.apple.com/legal/more-resources/phishing/) - there are various phishing receipt emails doing the rounds.

You can view the last 90 days purchases on your account (and optionally contact iTunes Support if you have a problem with a purchase) via http://reportaproblem.apple.com

You can only view your full purchase history via a computer's iTunes : See your purchase history in the iTunes Store on a Mac or PC - Apple Support

Hi Nanna,

if you have been billed for music start the iTunes Store App on your iPad and tab on "purchased" in the lower right corner in the App. You should see your purchases there. If not check if in your account if some purchases are hided.

...Helmut J....

The Purchased tabs in the store apps doesn't show when items were bought, and won't show items no longer in the store (nor hidden items nor items blocked via Restrictions)

Maybe this can help: https://buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/accountSummary