Very simple inspect html element

I have a site with custom html element and I need a Javascript line of code to refer to that element and get it attribute text data. If you work with custom html element, please have a look and get me the script to get the attribute in chrome console, something like `document.getElementsByTagName`
https://docs.google.com/document/d/1gEei8qg-57BLWFMrd3mcjl9mDk_bi5qNqScouJMCO6U/edit?usp=sharing
Thank you