Custom post type subtaxonomy template

I’m not sure what you mean about sub-taxonomies. Are you referring to the actual term? If so you could use the following to template it:

taxonomy-$taxonomy-$term.php

An example of this would be if I had a taxonomy called genres and a term called horror, I could then template this as:

taxonomy-genres-horror.php

Refer to the template hierarchy for more:

https://developer.wordpress.org/themes/template-files-section/taxonomy-templates/

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