From the product description page:
Jenkins is an award-winning, cross-platform, continuous integration and continuous delivery application that increases your productivity. Use Jenkins to build and test your software projects continuously making it easier for developers to integrate changes to the project, and making it easier for users to obtain a fresh build.
That makes questions about using Jenkins primarily a question about development tooling and although configuring Jenkins as a server is on-topic for ServerFault it is much more suitable for StackOverflow.
stackoverflow.com/help/on-topicstackoverflow.com/help/on-topic specifically lists "software tools commonly used by programmers" as on-topic.
If you look at the jenkins tag usage on ServerFault you'll see 270 questions tagged compared to in excess of 14'000 on StackOverflowStackOverflow, which seems to support that assumption.