Learn Portuguese (Portugal): Quando é a reunião?

Quando means when. Just like in English, it goes right at the beginning of the question before the verb. You don't need to change the word order or add extra helper words in Portuguese.

Why do we use é (from the verb ser) instead of está for a temporary meeting?

Even though a meeting only lasts a short time, we use ser (é) for events taking place. When asking when or where an event is happening, you will always use ser, never estar.

I see a before reunião. Are all words ending in -ão feminine?

Most Portuguese words ending in -ão are feminine, like a reunião (the meeting) and a televisão (the television). There are a few masculine exceptions like o pão (the bread), but guessing feminine is usually a safe bet for these words.