Try setting a condition like this.
New condition, select your character, select "Is animation playing", then set the animation he uses on the skill.
Add another condition (Press C) and select the character again, this time you will compare the frame the current playing, set it equal to the last frame of the animation.
After creating this two conditions set up your skill effect to appear wherever you want.
Remember to end the animation or set the conditions to trigger only once, or the game will create A LOT of skill effects one after the other.
You can use the same check frame condition to destroy the skill after it's used.