Knowledge is retained in the subconcious mind as a potentiality

And (remember)when your Lord brought from the Children of Adam, from their loins, their seed (or from Adam's loin his offspring) and made him testify as to themselves (saying) : "Am I not your Lord?" They said: "Yes! We testify," lest you should say on the Day of Resurrection: "Verily, we have been unaware of this." al-A'raf : 172

The Meaning of the Qur'an Vol IV : Abul a'la Maududi PP. 87-90
Based on the Qur'an & several traditions that the whole mankind that was born up to the Day of Resurrection was brought into existence at one and the same time and imbued with common-sense and brought forth in Allah's presence and asked to testify that Allah is their Lord.The Qur'an and al-Hadith describe this event as one which actually took place. We (the author) believe that this event actually took place in the physical world.The All-Powerful Allah, Who is bringing human beings into existence in the way he is doing now, has also the power to assemble all mankind before its birth and after its death.

The Covenant was taken from the whole of mankind for the reason: it was to make each and every individual fully and consciously responsible for his deeds so that those who would rebel against their Lord should be held accountable for their guilt. By taking this Covenant Allah has imbued in the heart of every individual that He alone is his Allah and Lord.How can this be justified when we do not remember it nor conscious of this Covenant? The answer is, its remembrance and consciousness has been removed from the memory and the conscious mind but it has been retained in the subconscious mind.

Its removal from the memory and the conscious mind is for the reason that the purpose of man's creation (test & trial) would not be rendered meaningless.It has, however, been retained in the subconscious mind as a potentiality, and can be brought into consciousness by intuition and internal factors as in the case of all other branches of subconscious knowledge. The fact that whatever man has achieved in culture, civilization, morality, sciences and all other aspects of human activities, lay hidden as potentialities and was brought out by external factors and intuition. But it ts also a fact that no education, no training, no environment, no external factor, no intuition is capable of creating any other thing than the one that already lies potentially in the subconscious mind.

The following is true for the branches of potential knowledge : All these exist as potentialities in our subconscious minds and prove their existence when they appear as actual actions. All potentialities require external stimuli, teaching and training to take practical shapes which, in fact, are a response of our potentialities to the external stimuli. All these things can be suppressed and made dormant by wrong desires and environment and perversions but can never be effaced totally from the subconscious mind. Therefore these can be reformed and converted by the help of inner feelings and external efforts. Exactly the same is true of the intuitional knowledge we have regarding our own position in the universe and our relationship to the Creator of the universe.