What types of wealth possessed by the questioner are subject to zakat, and is zakat due on the principal capital he invested in the company, or only on its profits?

Zakat (definition) is obligatory on money saved to pay installments and on capital used for trade, once a full Hijri year has passed, and the profit is zakatable along with its principal. As for outstanding debts, they are deducted from the wealth subject to zakat, though there is a difference of opinion among scholars on this matter. Zakat is not obligatory on residential apartments or plots of land unless they are intended for trade. In that case, they are appraised, and their zakat, which is one-quarter of one-tenth of their value, is paid when a full year has passed. If something is not intended for trade, or if there is hesitation about its intention, then no zakat is due on it.