If I have a light of frequency "x" and a generate another light of freuency "-x" and the 2 waves are superposed. Does the 2 waves cancel each other or does that light disappear?
Thank you.

You can't have a negative frequency O_o

Not negative but opposite

You mean pi radians out of phase, but the same frequency?

The resultant wave is still there, it just has zero net amplitude.

If the amplitude is 0, does the light disappears like sounds? If no, please tell me why?
Thanks

The light is not observable, but it is still there. Sound does not disappear when it is destructively interfering either - it's just that one wave is counteracted by another.

The NET amplitude is zero, but the individual waves still have amplitude and still exist.

Imagine having two jets of water in your face, one that's scalding hot and one that's ice cold. In the end, you get a face full of warm water, but the water is still there. Eh?