Is it possible to apply gold leaf on thick chalk powder-made thing?

Yes, that's possible. When you first apply it with a brush, the glue may absorbed into the chalk powder-made thing and it may not become sticky, but if you wait a while and then apply it several times, it will become sticky. This will allow the leaf to stick firmly.

However, if you apply too much glue, the glue may become sticky on the surface of the gold leaf. So, it would be nice if the amount of glue applied is just enough.