It's likely a made-up word, and the pronunciation would depend on the context and the person who created it.
Here are a few possible pronunciations, based on common English spelling rules:
* YOR-ki-lon: This is the most likely pronunciation based on the spelling.
* YORK-i-lon: This emphasizes the "York" part of the word.
* YORE-ki-lon: This pronunciation uses a slightly different sound for the "or" part of the word.
Ultimately, the best way to know how to pronounce "Yorkillon" is to ask the person who used the word.