We don't have visibility into third party systems, the best way is to search for unique identifiers (part of the listing job title, company name, job location, etc.), and don't forget to filter on attributes such as job type or categories, on the respective third party sites.
Please Note: Syndication is not immediate. It may take between 24 to 72 hours for a job listing to appear on other sites. If you have incomplete or inaccurate information (e.g. you don't have a minimum of 180 characters in your job description), your listing may not be processed by certain sites. If job listings are syndicated from another source - this also may interfere with indexing from our site.