What is the required amount of knowledge that each Muslim must acquire? What is the Personal Obligatory Knowledge of the Religion [Islam]?
It is not obligatory on every Muslim to seek all of the knowledge pertaining to the Religion of Islam. However, there is an amount of knowledge that each accountable Muslim must seek to acquire. The scholars of Islam refer to this knowledge as The Personal Obligatory Knowledge.
The Personal Obligatory Knowledge of the Religion is the amount of knowledge that each accountable person (mukallaf) has to learn about the fundamentals of Islamic Belief, acts of worship such as Purification and Prayer, Fasting, and some other Religious Rulings. Included in that are Rulings related to Dealings for those who engage in transactions.
Other issues about which one must know include the sins of the heart and of the other body parts, like the tongue, for example. The one who is obligated to pay Zakah is obligated to learn the details of paying it. Likewise, learning the details of Pilgrimage (Hajj) is obligatory for the one who is able to perform it. The Prophet, salla-l-lahu ^alayhi wa sallam, said:
“طلب العلم فريضة على كل مسلم” رواه البيهقي.
This means: “Seeking the Obligatory Knowledge of the Religion is an obligation upon every Muslim,” narrated by al-Bayhaqiyy.