Which words best complete this dialogue? —¿ vas ir al cine y con quién? —voy el viernes con manolo.

¿ vas ir al cine y con quién? 
Voy el viernes con Manolo.

Translation:

"[blank] are you going [blank] go to the cinema and with whom?"
"I'm going on Friday with Manolo."

The second piece of dialogue states the day the speaker plans to go to the cinema (Friday), so we can infer that the opening part of the first line of dialogue asks when the speaker is going to the cinema. Intuitively, the second blank should be filled with "to". In full, the sentence is as follows.

"When are you going to go to the cinema and with whom?"

"When" in Spanish is cuándo. A would go in the second blank.

¿Cuándo vas a ir al cine y con quién?

The words to complete this dialogue are cuándo and a.