What is this. Black small spots ,non movable, like poop of some kind of insect . Also leaves having greasy spots may be.

Shrikant Nichat Black Citrus Aphid Please check this link for more details and preventive measures.

It may be mold along with something else.

It's a poop of whitefly and it will invite fungus that turns leaves covered with black ash like substance. It is a fungus.