What is meant by "the general Muslim populace" in the definition of "that which is known by necessity from the religion"? And is Hajj known by necessity from the religion despite some elderly people being ignorant of it? And can what is known by necessity from the religion differ with the variation of time and place? And is there something that is known by necessity from the religion in all times and places and for all Muslims, and what are its examples?

The term "general Muslim populace" refers to the majority or most Muslims who have not received formal religious education. The concept of what is "known by necessity" in religion is relative, varying with times and places. Thus, something might be known by necessity in one era but not another, or in one place but not another. An example of this is that some elderly men and women may not know that Hajj is an obligation and a pillar of Islam, even though it is considered known by necessity in most Islamic environments and eras.