If God was thoroughly acquainted with evil before or apart from creation, then I submit that evil did not find its genesis in creation but in God. In that case, God did not "discover" it in creation, for evil was part of his thoughts quite apart from the existence of creation. It would have found it's way into creation reflectively rather than formatively. That seems an impossibility to me because evil is intrinsically at odds with God.
By Christ's argument, a house divided against itself cannot stand, so neither could God stand if he was for himself (good) and against himself (evil) within his own thoughts.
Therefore, evil could not have been in God's conceptions apart from those which instantiated creation. Even then, it could only have been so in general terms; i.e. "if we make creatures in our image they will do as they will rather than as we will." If evil was a subject thoroughly plumbed in God's mind apart from creation, then God's thoughts would be of evil to some extent and he would not be good, and he would not be pure. The evil that ended up being produced in the minds of mankind would exist as a reflection of the mind of God who made them rather than as an negative consequence of freewill.
Evil is a consequence of freewill, but it cannot be intrinsic in the created, pristine possessor of that freewill without it indicting the creator for it. Adam and Eve were created good and upright. Evil came their way afterwards, when they opted for their own wills instead of God's will (evil=anything against the will of God). Evil is only possible if there is a freewill apart from God's, but evil does not actually exist until (and unless) freewill is exerted in opposition to God.
A mind endued with such freewill would be transparent to God in all its evil, once it existed, because he is omnitemporally omniscient in regard to creation. Furthermore, all the minds that would ever come into existence would be transparent to God in all their evil, once creation was in place. However, if God omnisciently knew the evil thoughts of mankind from all eternity, that is, apart from creation being put in place, it would mean that something which could not come from God's own thoughts (they're not evil) and which only came into being temporally, informed God's knowledge eternally.
If God is pure and holy as the Word avows, and he actually regretted making mankind and was astonished at the depths of Israel's sin as presented in his Word, it is impossible that evil (whether his or ours) was part of his personal, eternal knowledge. The knowledge of evil, by necessity, is confined to and informed by the decision to create man in his image. If God had not created, he would not have any knowledge of evil. The existence of evil demands that God be aware of it by observation rather than by cogitation.
We may live in a universe that is quantumly frothy, but it seems to me that we must be careful in our explications of God's omniscience to accurately describe what is and isn't in the mind of God, lest we suggest something that would, by necessity, annihilate itself.