On
https://www.dokuwiki.org/template:dokuwiki was written that :logo.png (beside :wiki:logo.png and images/logo.png) is possible.
But it isn't..
https://github.com/splitbrain/dokuwiki/blob/master/lib/tpl/dokuwiki/tpl_header.php#L23
favicon and touchicon are detected on all three places, so adding :logo.png seems consistent with this.
https://github.com/splitbrain/dokuwiki/blob/master/inc/template.php#L1675