Because I'm using a logo in my header, I don't need the title-text. But I would like to have a browser-title. So I need to set a title and have to hide it in the header - but how?
I assume that your wiki looks like dokuwiki.org (meaning that you are using one of recent versions and default template). If not the approach still should be the same, search for $conf['title']
in your template.
There is a block in lib/tpl/dokuwiki/tpl_header.php:
// display logo and wiki title in a link to the home page
tpl_link(
wl(),
'<img src="'.$logo.'" '.$logoSize[3].' alt="" /> <span>'.$conf['title'].'</span>',
'accesskey="h" title="[H]"'
);
Remove <span>'.$conf['title'].'</span>
from it.
Each update of Dokuwiki engine will overwrite this change. You'll need to repeat it manually after each update or copy paste doku template into a new one and update this new template manually.