What is the criterion by which a legally responsible individual knows whether he has exerted his utmost effort in learning what is obligatory and forbidden for him in matters of the Islamic religion?

Knowledge is of two types: an individual obligation (fardh al-ayn) that every legally responsible person must learn, such as knowing what Allah has commanded; and a communal obligation (fardh al-kifaya) that the Ummah as a whole must undertake, which is whatever exceeds the individual's basic needs. For the legally responsible person to know if they have exerted their utmost in learning, they must exert all their effort to acquire the knowledge that is obligatory upon them. This capacity varies according to individuals, places, and times. Thus, what is obligatory upon scholars and those raised in a land of knowledge differs from what is obligatory upon ordinary people and those raised in a land of ignorance.