How is zakat paid on shares subscribed to in Bank Albilad three years ago, and in a new company a few months ago? And is zakat obligatory on the latter amount if it is not known whether a year has passed on it?

If the bank is usurious, then the profits must be disposed of by spending them on the welfare of Muslims, and you are entitled only to the principal. If your father did not pay zakat on it, then zakat for the past three years is obligatory. However, if the bank operates according to Sharia-compliant dealings, then the zakat on shares is the zakat on trade goods. They should be appraised, and one-quarter of one-tenth (2.5%) of their value should be given. As for the money saved in the company, if a year has passed over it, zakat becomes obligatory; otherwise, it does not. If the matter is not clear to you, the default is that a year has not passed. It is recommended to pay zakat as a precaution, in which case it would be an expedited zakat, which is permissible according to the majority of scholars.