"Co ty víš o Češkách?"

Translation: What do you know about Czech women?

[Shathu_Entayla]

Why is it "women"?

[AgnusOinas]

• o českých ženách = o Češkách
• o českých mužích = o Češích (that's also simply "about Czechs")

singular:

• o české ženě = o Češce
• o českém muži = o Čechovi

[endless_sleeper]

Cause it's plural :o

[JanisaChatte]

So češi would be "czech men" then ?

[MarcinM85]

Yes, but in this case (locative) it is o Češích.

[ken55414]

Is the "ty" really necessary?

[AgnusOinas]

The meaning is a little shifted here. "Co víš o...?" is a regular question "What do you know about...?"

With the added "ty" it's usually (also depends on intonation) a rhetorical question, roughly meaning "You actually know nothing/little about..."

[BoneheadBass]

It's not. But it can be used for emphasis.