In Job 1+2 Satan doesn't ask for forgiveness, he has a challenge for God, to show Him up by paining Job. I don't have any scriptural quotes for Satan asking for forgiveness, but in Revelations, he gets thrown into the pit for 1000 years, and still an army comes up to challenge Christ, with Him in view, in our presence.
I have asked God to forgive Satan for the things he has done to me, so that I can let it go. But as of late, Jesus has made it clear that for one to obtain the Holy Spirit, one has to have the thoughts (priorities) of another higher than yourself. Satan does not fit this bill. This is why forgiveness comes so hard to most folks. We grew into a world of "me first" and leave the others in the dust. Huge change of mind set, and heart set.
If Satan ever did repent, I'm not so sure that God would forgive him, as Satan knew the real deal from the beginning, as did the other angels that followed him. We don't have this same pespective, but we are called to be more than selfish, and give, even to those that do us harm.
The biggest miracle I have seen, is a person whose heart has changed from "me" to "you" first. Haven't seen it much, but boy howdy when it happens, watch out!