mkdocs_macros_plugin | Create richer and more beautiful pages

The answer depends on which version of MkDocs you are using. In #1376 the path was added to the config object as the attribute config.config_file_path. However, that won't be available until the next release (1.0). Regardless, earlier versions include an undocumented config option config['config_file_path'] which holds the location of the file. Be careful however, as any undocumented features are subject to change without notice.

As for the location of the Markdown file, that is available in various attributes of the page object passed to the plugin event. You have your pick of page.input_path, page.output_path, page.abs_input_path, and page.abs_output_path. Again, these are undocumented and subject to change in a future release without notice. In fact, #1504 proposes changing them to page.file.src_path, page.file.dest_path, page.file.abs_src_path, and page.file.abs_dest_path for the 1.0 release. But that's the risk in working against pre-1.0 software. Things change as the developers try to get it right. The good news is that the 1.0 release will lock these things down going forward.

Full disclosure: I am a member of the MkDocs development team.