Learn Arabic (Modern Standard): هل البنوك مغلقة الآن؟

The singular is بنك (bank). The plural بنوك (bunook) is a 'broken plural.' Instead of adding a regular ending like we do for human plurals, the inside of the word breaks apart to add the letter و (waaw) before the final letter. You will see this specific shape very often.

Why is the adjective مغلقة (closed) in the feminine singular form instead of a plural form?

This is a very important rule in Arabic: all non-human plurals (like banks, books, or cars) are treated grammatically as feminine singular, just like 'she'. Because البنوك are non-human, the adjective describing them must take the feminine singular form.

Where is the word 'are' in this sentence?

In Arabic, we do not use the verb 'to be' (am, is, are) in the present tense. To ask 'Are the banks closed', you just use the question word هل followed by placing the subject (البنوك) right next to the adjective (مغلقة).

What is the wavy symbol on top of the Alif in الآن (now)?

That wavy line is called a madda (آ). It represents a stretched out 'aa' sound. It usually happens when a regular Alif meets an Alif with a glottal stop, merging them into one long sound.