Default Working Directory: /home/runner/work/<repo-name>/<repo-name>
Variable Name: GITHUB_WORKSPACE

The same directory is also used by the checkout action
Before the checkout action, clones a repo the content of working directory is cleared

Docker Actions

Docker Actions can only to executed on Linux Runners

# Execute permission for script file
git update-index --chmod=+x entrypoint.sh

When using Docker action the working directory is mounted as a volume. If any directories are created in the container it will be usage in the next steps

In the Container the Working Directory is mounted at /github/workspace/

Composite Actions

The files that where included along with the composite action repo can be accessed at /home/runner/work/_actions/repo-owner/name-of-action-repo/ or using GITHUB_ACTION_PATH variable

Variables - GitHub Docs

Contexts - GitHub Docs