"When do you have to go to the office?"
Translation:¿Cuándo tienes que ir a la oficina?
Tener que is joined ie. tengo que, tienes que (have to). Similar to 'ir a' ie. voy a, vas a (go to).
'Debe' is a form of 'deber', which essentially means 'should' 'must' 'ought to', etc.
So more than once the system has given a form of deber in the answer without ever introducing me to it or defining it. It's very frustrating.
'Ir a' is joined and means 'to go to'. Voy a - I am going to. Vas a - You are going to etc.
The second verb goes into the infinitive - it would be 'Cuando tienes que ir a la oficina'. Also, as oficina is feminine, it's a la. Al is for masculine nouns only.