Is zakat obligatory on a financial deposit designated for repaying a loan, knowing that it is part of the debt and does not cover it entirely, if a year has passed over it?

You must repent to Allah Almighty for borrowing with usury, and for depositing money in a usurious bank if it is such. You should strive to get rid of the usurious loan and withdraw your deposit from the usurious bank and invest it in a permissible matter. Zakat (definition) is obligatory on the deposited money because it is still in your possession. If the debt reduces the nisab (definition), then there is no zakat, but if it does not reduce it, then zakat is obligatory on what exceeds it.