Perception
If your character is a spellslinger, he or she will have a way to perceive magicka, else they could not interact with it. How exactly that works is entirely up to you, althogh you might want to come up with something, even if it's just for the sake of talking to other wizards.
The way that works can include any of the senses, or something entirely else.
Some examples:
- Sight: Magicka could be perceived as colour, or smoke, or patterns of interwoven lines.
- Touch: Magicka can be felt on/under your character's skin, or like air pressure
- Taste: Depending on the magicka, your character has a distinct taste that they can learn how to work with
- Hearing: Magicka could be sounds, or noise, harmonies or rhythms
- Smell: Your character could - literally or not - smell magicka, or show hayfever-like reactions to it.
- Emotional reactions: Different spells make your character resonate - destruction makes them angry or afraid, restoration calms them down...
Disclaimer: Please do not go Anakin Skywalker on this. He's not an interesting character but a joke.
Of course by picking one way to perceive magicka, you settle with a way how your character casts spells - if you hear melodies, then your character would have to enforce a song upon the world to create the resonance which then becomes a spell.
Please keep in mind that this would be a sense that your character has had for their whole life, although it's possible they didn't pay much attention to it.
