The master location for hostname is /storage/.kodi/userdata/addon_data/service.libreelec.settings/oe_settings.xml .. but you'll only see the xml node for hostname if it has been manually added or changed via the GUI. Other services read the hostname from this location to set /etc/hostname (which is a symlink to /storage/.cache/hostname) at boot time.
XML
<?xml version="1.0" ?>
<libreelec>
<addon_config/>
<settings>
<system>
<wizard_completed>True</wizard_completed>
<hostname>WP2</hostname>
</system>
<connman>
<wizard_completed>True</wizard_completed>
</connman>
<services>
<wizard_completed>True</wizard_completed>
</services>
<about>
<wizard_completed>True</wizard_completed>
</about>
<libreelec>
<wizard_completed>True</wizard_completed>
</libreelec>
</settings>
</libreelec>
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