how do you know if there is vat on items purchased from itune?

http://www.apple.com/legal/internet-services/itunes/uk/terms.html#SERVICE says:

'Your total price will include the price of the product plus any applicable VAT (in effect on the day of download).'

I don't know about VAT receipts, you'd have to contact Support to ask about that.

http://www.apple.com/uk/support/itunes/ (or the equivalent for your country if different)