"Whose new bicycle is this?"

Translation: Kinek az új biciklije ez?

[MitjaSterman]

When owner is not known, the noun takes ending for 3. person singular?

[vvsey]

"Who" is by nature a third person, so, yes. But in Hungarian it can also be in the plural.

[Ishana92]

why is (is it) az required before uj biciklje? Is it because there is uj in front of it?