would know
No le sabría decir exactamente.
I couldn't tell you exactly.
Si Juliette estuviera acá, ella sabría del tema.
If Juliette were here, she would know about it.
— La gran juerga (1966)
Nunca sabría lo cerca que estuvo de que le mataran.
He would never know how close he came to being killed.
— Uno de los nuestros (1990)
Si la hubiese matado, sabría que es una trampa.
If I had killed her, I would know it's a trap.
— No se lo digas a nadie (2006)