It could be a made-up word, a name, or a word from a fictional language.
To figure out how to pronounce it, you'd need more context:
* Is it part of a book, game, or other work of fiction? If so, the author might have provided a pronunciation guide.
* Is it a name? You could try looking for the origin of the name.
* Is it a word from a made-up language? You could ask the creator for the pronunciation.
Without more information, it's impossible to say how to pronounce "asulon".