Editing field twig template for taxonomy term
The field type for taxonomy terms is entity-reference. You can use the field type for the naming of the field twig:

field--entity-reference.html.twig


Because there may be more than one reference field, it is more specific to use the field name, for example a twig for the preinstalled tags field:

field--field-tags.html.twig


If you want to use the target entity of a reference field as theme suggestion you would have implement this in a hook.

Edit acc. to the clarification:

If the field is inside of a taxonomy term, you have to add one more detail, either the field name or the name of the vocabulary:

field--taxonomy-term--field-body.html.twig
field--taxonomy-term--tags.html.twig