I'm not sure which maker you are using, but every event command can be found in the Game_Interpreter class (or Interpreter class in RMXP). I don't have any version of RM installed on my present computer, but it is probably something like this in RMVX:
$game_actors[x].skills.include?(y)
Where x is the ID of the actor, and y is the ID of the skill.
But you should look at the interpreter class in whichever version of RM you are using. That will probably have the best way to do it.