The Angelic Host, including those that fell from grace, were part of the created order. Therefore their intelligence and knowledge does not approach the infinite perfection of intelligence and knowledge found in God. Satan does not know everything by his essence. However God does by His uncreated divine essence. Remember that Satan did not even know Jesus was God incarnate when he tested him in the desert.
Below are two excerpts from the Summa Theologica on the subject of Angels
The angel’s essence, however, does not comprise all things in itself, since it is an essence restricted to a genus and species. This is proper to the Divine essence, which is infinite, simply and perfectly to comprise all things in Itself. Therefore God alone knows all things by His essence. But an angel cannot know all things by his essence; and his intellect must be perfected by some species in order to know things.
The future can be known in two ways. First, it can be known in its cause. And thus, future events which proceed necessarily from their causes, are known with sure knowledge; as that the sun will rise tomorrow. But events which proceed from their causes in the majority of cases, are not known for certain, but conjecturally; thus the doctor knows beforehand the health of the patient. This manner of knowing future events exists in the angels, and by so much the more than it does in us, as they understand the causes of things both more universally and more perfectly; thus doctors who penetrate more deeply into the causes of an ailment can pronounce a surer verdict on the future issue thereof. But events which proceed from their causes in the minority of cases are quite unknown; such as casual and chance events.
In another way future events are known in themselves. To know the future in this way belongs to God alone; and not merely to know those events which happen of necessity, or in the majority of cases, but even casual and chance events; for God sees all things in His eternity, which, being simple, is present to all time, and embraces all time. And therefore God’s one glance is cast over all things which happen in all time as present before Him; and He beholds all things as they are in themselves, as was said before when dealing with God’s knowledge (Q. 14, A. 13). But the mind of an angel, and every created intellect, fall far short of God’s eternity; hence the future as it is in itself cannot be known by any created intellect.