Is zakat obligatory on money acquired from an interest-based source, without knowing the amount of the interest, whether the owner of the money is a Muslim or an apostate?

It is permissible to benefit from the father's money, even if it is usurious, because it is mixed money. The disposal of an apostate's wealth before his repentance is a matter of scholarly disagreement. As for the zakat (definition) on money gifted by the father, zakat is obligatory if it reaches the nisab (definition) and a year has passed since its ownership. This is with a reminder of the seriousness of declaring someone an apostate, the obligation to be dutiful to one's father even if he apostatizes, and calling him to Islam with wisdom and good admonition.