How to know if my XML Sitemap being submitted?
If you are using Drupal 7, it will show that your sitemaps have been submitted in your log messages at Admin > Reports > Recent Log Messages (/admin/reports/dblog)

Click on "Filter log messages" and select "xmlsitemap" 

If you do this, it will show when the last sitemap was generated and when it was submitted the the search engines that you have configured it to submit to (in my case, Google and Bing).