My requirement is whenever developer try to do check-in existing GitLab repository then before doing check-in in repository,build should trigger (Jenkins build) and Junit test case should run on new check-in and if passes then it should go forward and will allow developer to do check-in in main repository.
I am not sure but is pre-hook commit can achieve this requirement?
While you could achieve this with pre-commit hooks, it's more common to do so with post-commit hooks on the server-side.
You can achieve this by operating a branch based workflow, there are multiple to choose from - I would recommend reading through this guidance by Atlassian.
Developers will create branches from a 'main' branch (often master, but can be a 'dev' branch working towards a release for instance), then develop code on that branch. They will then push their branch and commits to the remote repository (GitLab). When ready to merge into the main branch, your developers can open a merge request onto the main branch.
On GitLab you can setup a webhook to trigger Jenkins builds when a push event occurs. I would recommend this guide to guide you through it.
In the GitLab project settings you can require a passing build before merge requests are allowed to merge.
Furthermore, your understanding of Git seems incorrect - check in is not a term used in Git. Please take a look at the Git documentation. In Git a developer creates commits against a local copy of the repository, then pushes these to a remote repository (GitLab/GitHub etc.). There is no direct equivalent of the 'check in' used in various centralised version control systems e.g. SVN.