How do you say is on in Spanish?

If you mean it litterally, as in, "The T.V is on" then it is "Esta encendido" (mas.) or,"encendida" (fem.) If you are trying to say "Oh, you wanna fight? then it's on!"T....then it's a very difficult question, since it varies a LOT in each country, state, region, citiy, and even within families