Translation:Vy jste o tom nevěděli?
"O tom jsi nevěděl?" gets corrected with "O tom jste nevěděl?, but shouldn't it be a possible translation?
Added now. Thanks.
Why is leaving out 'vy' marked wrong here.
'Jste' needs to be in the second position in the clause, if you leave out 'vy', you need to move it.