i want to know when my itunes gift card was redeemed

If you redeemed it onto your account try contacting iTunes Support and see if they can tell you when you redeemed it : http://www.apple.com/support/itunes/ww or https://www.apple.com/emea/support/itunes/contact.html

If it was redeemed onto somebody else's account they shouldn't be able to give you any information due to legal/privacy reasons.