Spell-Casting[2]
Although it seemed like he was staring at the instructor, he wasn't. His attention was rather taken by another system notification.
[Does the Host want to learn the skill "Lightning Stun"?]
[Cost: 5 skill points]
[Yes/No]
Harry was quite surprised by the notification that appeared in front of him. He hadn't expected that he would be able to learn new skills from spell-books
He planned to get the skill "Lightning stun" from the skill shop, so when the spell-casting class started, he would simply use the skill instead of learning or rather, casting the actual spell.
With 'mana core illusion' active, it would seem like he was actually channelling the required mana from his mana core and casting the spell.
As for how he knew 'Lightning stun' would be the skill he would be learning today, it was because it was common information that Lighting stun was the first spell Lightning Elementalists were taught in the academy.