* It's a misspelling: Perhaps you meant to type something else, like "Onyx" jewelry. Onyx is a popular gemstone used in various jewelry designs.
* It's a brand name or a specific designer's term: There might be a jewelry brand or a designer using "Onk" to describe their pieces. Without knowing the brand or designer, it's hard to determine the meaning.
* It's a niche term: It could be a term used within a small community or subculture related to jewelry.
* It's a neologism: Someone might have coined the term recently, and it hasn't gained widespread usage yet.
To help you find the meaning, can you provide more information?
* Where did you encounter the term "Onk jewelry"?
* Do you have any other context, like a website, an image, or a description?
* Are you sure about the spelling?
* Where are you located? Perhaps it's a regional term.
With more details, I can try to provide a more accurate explanation.