The only Skill you've used that takes MP is [Run-By-Strike], and you used it twice. So you have 7 MP left and can't use it again (it takes 8 MP)
Also I may have explained this, or I may not have, but ill explain it again regardless.
If it says (Active: Cost Here) then you say its name to use it and it has an MP Cost, HP Cost, or eventual other costs that can appear with certain other abilities available that you pay upon its usage.
If it says (Active), then you can use it and it has no MP Cost.
If it says (Passive), then it is always activated. No names or MP Costs are necessary.
If it says (Special), then it has special circumstances in which it is activated and no chanting is necessary unless it says so in its description.
Your Skill:
Sneak Attack (Lv 1: 0%) (Special): You know how to sneak up on enemies properly and deliver a quick, powerful strike to their vitals. Whenever you sneak up on an enemy and attack, you perform a Sneak Attack, which is a regular Attack that deals 50% more damage and has +1 Critical Range. To Level: Attempt, Successfully perform a Sneak Attack, Defeat an Enemy, Get a Critical Strike.
Activates whenever you sneak up on an enemy and perform a regular attack. You do not need to say its name.
Ill probably add this to the front page for future reference under Skills.
So you don't have to worry about saying your Skill name (you don't really have to shout them or speak them loudly for the world to hear, you just have to say them in a plain voice really, but who doesn't love shouting attack names). You can't mumble or whisper though.
But yea, your new Sneak Attack Skill doesn't have to be voiced to be activated. You just have to do what it says when they are (Special) Skills.