knows what they're doing
She knows what she's doing.
Tu hermana es grande, sabe lo que hace, Fede.
Your sister is grown-up; she knows what she’s doing, Fede.
— Nueve reinas (2000)
He knows what he's doing.
Y ya sabe lo que hace la gente al levantarse.
And now you know what people do when they get up.
— Abre los ojos (1997)
Parece que ese tipo sabe lo que hace, creo.
It looks like that guy knows what he's doing, I think.
— Sonidos vecinos (2012)
Tom no sabe lo que hace Mary para ganarse la vida.
Tom doesn’t know what Mary does for a living.
Él sabe lo que hace, así que déjalo continuar con el trabajo hasta el final.
He knows what he’s doing, so let him continue the work until the end.
Puede ser joven pero sabe lo que hace.
He may be young, but he knows what he's doing.
— Porco Rosso (1992)