"What does he do at the fair?"
Translation:¿Qué hace él en la feria?
I asked a Spanish speaking friend, who said that a is used for destinations or directions (eg. va a la feria) and en is used when you're talking about being at or doing something in a place (eg. Hace en la feria). So, montamos un caballo a la feria is we ride a horse to the fair, and montamos un caballo en la feria is we ride a horse at the fair (like you buy a ticket for a pony ride).
I have been taught that when referring to a person "at" a location Spanish always uses "en". Just a rule. But this sentence may be ambiguous because as phrased in English it could refer to what he is doing, like a job, "at" the fair? In that case, maybe, "a" would be right?? But I just stick with the rule.
In Spanish accented letters are completely different letters to non-accented, meaning qué and que are completely different words, just like sí and si. Qué means "what", while que sort of means "that". The phrase you have there is "what is it that he writes at the fair?", or in less clumsy English: "what does he write at the fair?".
I found this Spanish blog which explains the difference between 'que?' and 'cual?' . It has helped me so I thought I'd pass it on.