I required a means to print all variables. With the help of AI, I constructed such a partial, which I share here. Simply add {{ partial debug-page-vars.html . }} where you want a list of all your variables to be printed (Page, Site, front matter, Params). Enjoy!
P.S. It would be nice if Hugo made available a comprehensive set of debugging tools out of the box. Two features not available are: 1) the search order that determined which template file was chosen, and 2) the path to the template file used to construct the displayed web page.