Is zakat obligatory on an amount that has been impounded, and cannot be disposed of except by withdrawing 550 Euros per month, knowing that the impoundment occurred before the completion of the hawl (one year)?

Zakat becomes obligatory on money if it reaches the nisab (minimum threshold) and a hawl (full lunar year) passes over it, provided its owner has control over its disposal. If one cannot dispose of it, for example, if it is usurped or held by an insolvent person, then zakat is not obligatory until it returns to him, at which point he should pay zakat for all the preceding years. As for money that you temporarily cannot access due to studying, if you have other money from which you can pay zakat, then you must do so every year. Otherwise, the zakat remains a debt upon you, and you should pay it whenever you are able, unless this money will never return to you even if you stop studying, in which case there is no zakat due on you.