God did not ask Satan this for His own knowledge. By asking, He got Satan to reveal his own doings. We do need to remember that we do have a very powerful enemy and that he has a deadly agenda. Thankfully, through Christ, we can also have victory over Satan and his army of fallen angels. We are called to help others through the spiritual battle and even to accept help when we need to.
Something that does surprise me, did Satan actually answer God in truth? Can Satan lie to God? He did try to tempt Jesus with the actual Word of God, which is Truth, even if being used in a deceitful way. Of course, lying to God is pointless. We have so much to consider today! and every day! :)
Added thought, I wonder how long it takes Satan to roam once throughout the earth. He does have help. I'm not going to spend too much time thinking about it. Thankfully, God is omnipresent: om·ni·pres·ent | \ ˌäm-ni-ˈpre-zᵊnt \ Definition of omnipresent: present in all places at all times.
We also know this from Scripture: "Where can I go from your Spirit? Or where can I flee from your presence? If I ascend into heaven, you are there; if I make my bed in hell, behold, you are there; if I take the wings of the morning and dwell in the uttermost parts of the sea, even there your hand shall lead me, and your right hand shall hold me. If I say, "Surely the darkness will hide me and the light become night around me," even the darkness will not be dark to you; the night will shine like the day, for darkness is as light to you (Psalm 139:7-12). "