The Magical Striker feat is available to Sorcerers and Wizards.
It lets you enhance "a weapon you are wielding" (p. 132) for the next Strike you make that round, after you finish casting a non-cantrip spell.
Incidentally, some of the Sorcerer's bloodlines also grant you powers that bestow some form of unarmed attacks upon your character when activated.
This is notably the case of the Draconic bloodline, which grants dragon claws. These are unarmed attacks, agile and finesse, and your character is trained with them.
So far, so good.
On page 178, it is mentioned that unarmed attacks count as simple weapons.
However, no where does it say that you are considered to be wielding an unarmed attack.
In short, does Magical Striker work with unarmed attacks?
The feat specifies that "You siphon residual spell energy into one weapon you’re wielding".
Are you considered to be wielding a simple weapon when you have unarmed attacks or not?
I would say yes, because sorcerers don't need another boot in the ribs.
That was my initial reaction as well but do keep in mind this feat is also accessible to any class that takes the Wizard archetype.
Monks going into Wizard and picking up Magical Striker could potentially face the same issue.
Since unarmed attacks are simple weapons and fist is listed as a simple melee weapon that requires 1 hand to wield (p. 180), I would say that you are indeed wielding a simple melee weapon when you have the ability to make unarmed attacks.
At least I do believe that was the intent. By RAW however, I'm not seeing anything to support this, hence why I want other people's view about it. :)