The official github pages documentation explains how you can test your Github Pages using Jekyll locally. I had a hard time installing all dependencies. A faster and easier way is to use the docker image provided by Jekyll. Make sure you are using the image with the pages tag: jekyll/jekyll:pages.
I use below docker-compose file to start up an docker image with Jekyll which serves the current directory where I cloned my Github pages repository
version: '3'
services:
github-pages:
image: jekyll/jekyll:pages
volumes:
- .:/srv/jekyll
ports:
- 4000:4000
command: jekyll serve