come facevi a

how could you

→ come
phrase Rare #35,245
how could you Used to ask how someone was able to do or know something in the past; followed by an infinitive.
IT: Come facevi a saperlo?
EN: How could you know that?

Come facevi a sapere che ero qui?

How did you know I was here?

— Tempo d'estate (1955)

Come facevi a saperlo?

How did you know?

— Crimini e misfatti (1989)

Come facevi a sapere che era una nazi?

How did you know she was a Nazi?

— Indiana Jones e l'ultima crociata (1989)

Ehi, come facevi a saperlo?

Hey, how did you know?

— Trappola di cristallo (1988)

Come facevi a sapere tutto in anticipo?

How did you know everything in advance?

— I morti non muoiono (2019)

E come facevi a distinguere l'oceano da un lago?

And how could you tell the ocean from a lake?

— L'uomo che venne dalla Terra (2007)

Come facevi a esserne tanto sicuro, cazzo?

How the fuck were you so sure about it?

— I morti non muoiono (2019)