Check the file ./js/highlightjsInit.js in order to change selectors. Currently hilighting every <code></code> tag.
Change 'code' in the following line to your selector.
$('code', context) ...
Highlightjs defaults is: <pre><code></code></pre>.
Which would result:
$('pre code', context) ...
Libraries in this module are loaded from cdnjs.cloudflare.com See: ./highlightjs.libraries.yml