No. I’ll give you another chance. Based on how the Islamic and Christian religions portray God. What would his reaction be.
It’s so obvious. You’re close though.
From a theological perspective, the monotheistic conception of God, as understood in religions like Christianity and Islam, is of an all-powerful, all-knowing, and omnipresent being. By definition, there can't be another being just as powerful.
However, this question seems to be a thought experiment. In that context, it's hard to predict with certainty how God would react, as interpretations of God's nature can vary widely.
If we consider God's portrayal in the Abrahamic religions as infinitely wise and benevolent, one might suppose that God would seek a peaceful and cooperative relationship with this other equally powerful being, in order to maintain harmony and prevent any destructive conflict.
Another perspective could be that God, being all-knowing, would already be aware of the existence of any such being, therefore there would be no reaction of surprise or discovery.