I *think* that it's one of the inkjet transfer methods rather than laser; I've never tried inkjet transfers. However, the link I gave you earlier details the use of Damar varnish; there's some specifics here too - https://www.engravingforum.com/showthread.php?t=3141

Even more here - https://www.culverart.com/Engraving%...%20Process.pdf

As for transfer paper - it seems to be a term that means different things to different industries, which isn't entirely helpful. I note from the comments that he has to experiment with different brands...