Copy mages have the uncanny ability to observe magic and break it down into its component parts, allowing them to copy spells they have seen. As such, they have an easier time learning new spells than other wizards.

Arcane Mimicry

At 2nd level, you gain the ability to analyze and learn spells when you see someone cast them. As a reaction, when someone you can see within 60 feet of you casts a spell, you can make an Intelligence (Arcana) check against a DC of 15 + the spell's base level. For instance, if you were trying to copy a fireball cast with a 4th level slot, the DC would be 18 because fireball is a 3rd level spell. On a success, add the spell to your list of prepared spells.

To learn a spell this way you must be able to see and hear any somatic or verbal components, the spell must be in the wizard spell list, and it must be at least 1st level and of a level that you can cast. When you finish a long rest, the spell is removed from your list of prepared spells. You may copy the spell into your spellbook by spending time and gold, as if you were copying it from a scroll or another wizard's spellbook. Once you copy a spell this way, you can't use this feature again until you finish a long rest.