If your purchase is within the last 90 days, you can view it online as follows:
If you go to https://reportaproblem.apple.com and you are logged in with your Apple ID, you can view recent purchases, and print out the receipts, or email them to an address.
If your purchase is older however, I have found a way where you can request that a receipt for a purchase be emailed to you once again, but you cannot do it in your browser, it requires either an iOS device or a Mac with iTunes:
For iOS Devices (instructions as of iOS 11.4):
- Open Settings.app
- Tap on your name where it says "Apple ID, iCloud, iTunes & App Store" (it's the first item in the list)
- Tap on "iTunes & App Store" (it should show the email address of your App Store / iTunes account underneath)
- Tap on the first item at the top that looks like this: "Apple ID: your_email@your_domain.com"
- Choose "View Apple ID" from the list and authenticate if necessary.
- Scroll down and tap on "Purchase History"
- Choose your time range as necessary by tapping on "Last 90 Days".
- Find the purchase you need the receipt for, and then tap on the row that says "Total Billed: $XX.XX" and has the rightward pointing chevron/arrow. This will take you to the Order/Receipt.
- Scroll right to the bottom, and you will see a "Resent" button. Tap it, and a new copy of the receipt will be sent to the email address of your Apple ID.
- Open iTunes
- Sign in with your Apple ID if you aren't already (under the Account menu).
- From the Account menu in the menu bar choose "View My Account..."
- Under Purchase History, click on "See All".
- Choose the desired date range at the top left.
- Find the order that you need the receipt for and click on the number next to "ORDER ID" in the top right of the block for the order. This will expand the block to show more details of the order.
- In the bottom left of the expanded block (underneath your billing address) you will see a small link entitled "Resend". Click it and a copy of the receipt will be resent to the email address of your Apple ID.
Note: You can only resend receipts for purchases that actually have value and were billed to a payment method.
Based on instructions found in the following Apple Support Document: https://support.apple.com/en-us/ht204088