Consider the following:
This is John chapter 16. Jesus is addressing His disciples before His crucifixion.
“But now I go away to Him who sent Me, and none of you asks Me, ‘Where are You going?’ But because I have said these things to you, sorrow has filled your heart. Nevertheless I tell you the truth. It is to your advantage that I go away; for if I do not go away, the Helper will not come to you; but if I depart, I will send Him to you. And when He has come, He will convict the world of sin, and of righteousness, and of judgment: of sin, because they do not believe in Me; of righteousness, because I go to My Father and you see Me no more; of judgment, because the ruler of this world is judged."
This has been fulfilled: Jesus left the earth and He sent the Holy Spirit to the earth.
Now, the Spirit is doing three things to the world: convicting them of sin, of righteousness, and of judgement.
Conviction of sin is the awareness that the distance between man and God is insurmountable.
Conviction of righteousness is the awareness that a standard of life is found in Christ alone.
Conviction of judgement is the awareness that the ways of the world, and its unseen ruler, are corrupt beyond measure.
Notice that the conviction of sin is because "they do not believe in Me (meaning "Jesus")". Belief is a lifestyle, not a cognitive exercise. Here, in John chapter 16, the Holy Spirit has been sent to convict the world, to convince them without wavering, that their standard of life falls well short of the divine standard of Christ. They are made internally aware of a divine standard by the Holy Spirit.
Then, they are made aware that a righteousness has been revealed and finally, that the order of the world and its leader are corrupt.
In conclusion: there are no people who do not know God exists. There are only two types of people in the earth: those who do not obey God and those who obey God.