Why tuning fork of 256Hz will resonate with 512Hz frequency?

If a piano frequency is 256 hz on the right what is the frequency on the other side?

The frequency of a piano note is the same on both sides. If a piano key is producing 256 Hz on the right side, it will also produce 256 Hz on the left side. The frequency is determined by the pitch of the note being played, which is consistent across both sides of the piano.