We have a magician apprentice (let's call him Steven) and his master (Destionell the Great). Steven is serving for a long time to his master and he truly hates it.
Every day all his job is just cleaning Destionells house, cooking him meals and washing his robes. And all of that without the magic of course (because you're not ready yet, the master always say to Steven).
The apprentice actually never learnt a single spell and never saw a single book of them (the books are even enchanted so no one could open them without magicians knowledge), but Steven desires a hopes to be a great wizard, so he's not leaving his master despite all of this. Steven never saw his master casting any spell, but he believes him strongly, as he is well-known magician.
One day Steven came up with a plan. Because he was often delivering masters mail to the nearest village, he has access to some (unimportant) handwritings of his master. Also, he is sometimes cleaning the room when Destionell is writing some spells (with a regular pen on a regular paper like the magicians always do).
So Steven decides to learn how all the pen strokes and the gasps between words his master does sound. He will always listen very carefully and after a certain time, as he hopes, he will be able to find out more about some of the spells his master is writing, just by hearing.
TL;DR: Is it possible to learn to recognise what someone is writing just by hearing it (if you are practising with the same person)?