How is zakat paid on a stock portfolio that was sold with a deferred increase for a year and a half, and is the zakat on its original value at the time of sale or on the future value that the buyer will pay, knowing that the buyer has traded with its contents speculatively?

If a stock portfolio is sold for a deferred price, this price becomes a debt owed by the buyer, and it is subject to zakat (definition) as a debt. If the debt is owed by a solvent and willing payer, its zakat becomes due when a full year has passed. If the debt is owed by a procrastinator or denier, its zakat is not obligatory until it is collected, and a new year commences with it. Zakat is due on the deferred price that has become a debt owed to you by the buyer, not on the original value of the portfolio.