You can check the purchase history and order numbers of items you bought in iTunes Store / App Store by following the simple steps below:
Step 1: Open iTunes and click on Store >> View My Account
Step 2: Enter the Apple ID and Password when asked
Step 3: Scroll down to Purchase History and click See All
Here you will be able to see the history of all items you purchased via App Store or iTunes Store.
Note: In case if you have not signed in to iTunes Store, sign in using your Apple ID to see View My Account.
You can also view the purchase history by simply clicking on iTunes Store appearing at the far left panel, and click your account name appearing at the far top right.
You can view the detailed history of purchases made on a single day by clicking on the small arrow appearing beside the Order Date.