Learn Portuguese (Portugal): Onde é a saída?

In Portuguese, we generally use the verb ser (here, é) for permanent locations. Because an exit is a permanent part of a building, we use é. The other verb for "to be", estar, is used for temporary locations (like asking where a person or a movable object is right now). You will also often hear the verb ficar used for permanent locations.

I sometimes see aonde used for "where". Why is it just onde in this sentence?

Onde means "where" (in or at what place) and is used for fixed locations. Aonde means "to where" and is used when there is movement or a destination involved, usually with verbs of motion like going or traveling. Since we are just asking where the exit is located, we use onde.

Is the word saída related to a verb?

Yes! A saída is a feminine noun meaning "the exit" or "the departure". It comes directly from the verb sair, which means "to leave" or "to go out".