wouldn't know
Yanni no sabría decir si la voz era masculina o femenina.
Yanni wouldn't be able to say whether the voice was male or female.
Si no fuera por tu consejo, no sabría qué hacer.
If it weren't for your advice, I wouldn't know what to do.
Cosas que no sabría de no ser el asesino.
Things I wouldn't know if I weren't the killer.
— Memorias de un Asesino (2003)