What should I do concerning the zakat on money that I possessed for 10 years and have now spent, knowing that I am currently unemployed, and should I pay it from my salary if I return to work?

As long as zakat (definition) became obligatory upon you, with the ability to pay it, it remains a debt upon you that you should pay whenever you are able. So, if you acquire money, you are obligated to pay the zakat that became due. The way to determine what is due upon you is to ascertain the amount of money you possessed each year separately. If it reached the nisab (definition), then pay the obligatory amount. You must be cautious in this regard until you are reasonably certain that you have cleared your obligation. The nisab for current banknotes, at which zakat becomes obligatory, is the equivalent of twenty mithqals of gold, which is estimated to be approximately eighty-five grams in current weight. The amount that must be paid is one-quarter of one-tenth: 2.5%.