"Které koleno vás bolí?"

Translation: Which of your knees is hurting?

[SerhiyBila]

Why is ''Which of your knees aches?'' not correct?

[BoneheadBass]

Alternatives with forms of "ache" have been added.

[MartinSandom]

Is this translation correct? I don't know how you get 'of your knees' from the Czech. I would translate it as Which knee hurts/is hurting you.

[VladaFu]

Both are accepted.