¿Que lo reconociste?

[Tyrn]

Hi,

You recognized him?

Why que?

[Rusty]

reconociste

That que is a conjunction or a relative pronoun (notice there's no accent mark, which it should have if it were an interrogative pronoun).

This phrase would usually be asked to either determine what was meant, or reinforce what was meant. The context should make this clear.

[AngelicaDeAlquezar]

I agree with Rusty.
Also, to me, it kind of elides a word to make a "more complete" sentence:
- ¿Dices que lo reconociste? -> Are you saying you recognized him?
- ¿Cómo que lo reconociste? -> ¿How is it that you recognized him?
- ¿Es que lo reconociste? -> Is it true you recognized him?


In Mexico you're more likely to hear "¿Lo reconociste?", but in other regions and in higher registers the "que" is added naturally. :)

Side note: There is also:
- ¿Qué, lo reconociste? -> So, did you recognize him? ;)