no sabían qué hacer

didn't know what to do

→ no
phrase Rare #38,612
didn't know what to do Uses the imperfect tense of saber and usually refers to something that was true in the past. The subject is understood from context and may be they or you formal plural.
SP: Los estudiantes no sabían qué hacer después del examen.
EN: The students didn't know what to do after the exam.

Ellas no sabían qué hacer con él.

They didn't know what to do with him.

No sabían qué hacer con él.

They didn't know what to do with him.

Ellos no sabían qué hacer con él.

They didn't know what to do with him.

Tom y Mary dijeron que no sabían qué hacer.

Tom and Mary said they didn't know what to do.

Los granjeros no sabían qué hacer.

The farmers didn’t know what to do.

Ellos no sabían qué hacer primero.

They didn't know what to do first.