"Whose sheet of paper is this?"
Translation:Czyja jest ta kartka papieru?
yes but then there are "normal sentences", less normal sentences, poetic sentences and incorrect sentences. Your one is either less normal or poetic. I cannot imagine a situation or a question for it.
Kartka jest Kasi vs Kasi jest kartka -The sheet is Kasia's
Kartka Kasi jest vs Kasi Kartka jest vs Jest Kasi Kartka vs Jest Kasi Kartka -Kasia's sheet is (here)
"To" is a dummy pronoun, which can replace the verb, so if you choose to use the demonstrative pronoun "ta" instead, the verb needs to be included. Therefore it's either Czyja jest ta... or Czja to....
Occasionally you might hear the version that you typed in, but that's very colloquial and we don't accept it here.