What is the ruling on Zakat for shares that were purchased for profit, their price has doubled, and their Zakat has not been paid previously?

You must inquire about the ruling on shares before purchasing them, because their ruling depends on the company's activity. If its activity is prohibited, or its dealings are based on usury, then investing in it is forbidden.

As for the zakat (definition) on shares, it has two cases: 1. If the purpose of investing is to benefit from the income generated by the shares, and they represent fixed assets, then only the profits are subject to zakat, provided they reach the nisab (definition) and a full year has passed over them. 2. However, if the shares represent trade goods, then the zakat is 2.5% of both the capital and the profits. Similarly, if the purpose of investing is to trade in the shares themselves, then they are subject to zakat on trade goods, by paying one-quarter of one-tenth of their market value at the end of each year.