In Jenkins, you can install TestNG Results Plugin.
Once you install plugin, when you create/ modify a job that generates TestNG result, you can add a post-build action "Publish TestNG Results".
It will ask you for XML pattern, you can enter "**/testng-results.xml" there and save it.
Now, when you execute a job that generates TestNG report will have an option to see "TestNG Results" on the execution page.