Variable: org-html-footnote-format
org-html-footnote-format is a customizable variable defined in
ox-html.el.gz.
Value
"<sup>%s</sup>"
Documentation
The format for the footnote reference.
%s will be replaced by the footnote reference itself.
Source Code
;; Defined in /usr/src/emacs/lisp/org/ox-html.el.gz
(defcustom org-html-footnote-format "<sup>%s</sup>"
"The format for the footnote reference.
%s will be replaced by the footnote reference itself."
:group 'org-export-html
:type 'string)