Is zakat due on gold purchased for the purpose of selling when necessary, along with the annual money zakat, or is it subject to zakat in a coming year?

The gold you bought should be subject to hawl (the passage of a full lunar year) based on the price you paid for it, whether that was in circulating currency, gold, or silver. This is because purchasing it does not interrupt the hawl for zakat. Currencies are treated like gold and silver in terms of zakat rulings; they are considered a single type of wealth. The questioner must pay zakat on the gold along with the rest of his wealth when the hawl is completed, provided the total amount reaches the nisab (minimum taxable amount) and a full year has passed since the price used for the purchase. Ibn Qudamah stated that exchanging the nisab for a different type of asset interrupts the hawl for zakat, except for gold exchanged for silver or for trade goods, because they are considered a single type of wealth. Trade goods are combined with monetary wealth for the purpose of the hawl.