Is Zakat obligatory on money that has reached the Zakat threshold but is subject to debts exceeding it, knowing that it is placed in savings certificates to pay installments of a deferred debt? And is Zakat obligatory on ornamental jewelry that may be sold to pay installments of the same debt?

As long as the debts consume the money, there is no zakat (definition) on it, unless there are other assets exceeding the need, such as real estate or a car. In that case, these assets are used to cover the debt, and the money is then subject to zakat. As for women's jewelry intended for adornment, there is no zakat on it according to the majority of scholars.