He knew

And he said, Who told thee that thou wast naked? Hast thou eaten of the tree, whereof I commanded thee that thou shouldest not eat? (Genesis 3:11 KJV)

God knew without even asking that Adam and Eve ate the fruit. But he still asked cause he wanted them to confess what they had done. When we know we have sinned we shouldn't try to hide it God knows anyway, but God wants to hear our confession even if he already KNOWS what we have done, Just like king David when he was caught in adultery with Bathsheba, he immediately cried out for God to forgive him. God will still forgive you even if it takes a while for you to finally confess, but how blessed it is when we immediately confess and ask for forgiveness it is truly wonderful to know I am forgiven.