I dont have a source to quote, but in all TCG I judged, there is a common sense applied to what is known and unknown to a given player.
In that case, as the card was choosen from your hand, and was never seen by your opponent, you know what the card is, so you are allowed to look at it again. But your opponent cant.
For the same reason, both player can lool at both discard piles, as all cards put to the discard pile have usually been played before and the fact they were sent to the discard, is public.
Same thing if you want to know how many cards a player has in hand at a given moment, how many cards are left in either deck.
Same if I ask my opponent something that was public, like if he crafted a key on the previous turn or not, how many cards are currently in his archives.