Well, the title question is straight-forward. Elemental Affinity states
Starting at 6th level, when you cast a spell that deals damage of the type associated with your draconic ancestry, add your Charisma modifier to that damage.
For example, Wand of Fireballs states
While holding it, you can use an action to expend 1 or more of its charges to cast the Fireball spell (save DC 15) from it.
Note that Elemental Affinity does not require the Cast a Spell action, however, it requires that you are the one casting the spell. Does it count if it comes from the magic item? I feel that this should be an easy answer but I'm a little confused here.