Actually it is a War Mage Only card.
So any mage who is trained in the war school at level 2 or more can slot this in their book 
Where do i find this (very interesting) information?
My rulebook says:
Training
Your Mage is trained in one or more schools of magic. These
are the spells that are easiest for your Mage to learn. If you
add a spell from a trained school into your spellbook, you
must spend spell points equal to the Level of the spell.
If you add a spell from a school your Mage is not trained
in, you must spend Spell Points equal to twice the Level of
the spell.
Spell TraitsT hat Affect Your Spellbook
School of Magic Only: Some spells can only be cast by a
Mage that is trained in a specific school of magic. You may
only include these spells if the Mage you are playing has the
proper training.
For example, the Temple of Asyra says Holy
Mage Only, so only Mages trained in Holy magic, like the
Priestess, can use this spell.
