Given that Laser disc players do not have a digital output, there is no way to "read" the laser disc data to convert it into CDG format.
The only thing I could suggest is to try to copy the audio and video onto a Video CD (VCD format) disc. This is very different from CDG.
I once found a product that would take a video and audio signal from VHS (or Laser disc) and write a VCD disc.
However... it only wrote a single track on the disc! Thus, if you had 15 songs, you would not be able to access them except playing all the way through from the first! I don't think that is a usable product for karaoke performance.
