The description that is set in the general settings is not displayed on course section even though the checkbox is checked.

My research shows that this happens due to a condition in the Moodle file lib/modinfolib.php.

Line 924
// When there is no modname_get_coursemodule_info function,
// ... but showdescriptions is enabled, then we use the 'intro',
// ... and 'introformat' fields in the module table.

The function "questionnaire_get_coursemodule_info" in mod/questionnaire/lib.php doesn't implement a "showdescription" part

I added this lines, seen on mod/page

if ($coursemodule->showdescription)

{ // Convert intro to html. Do not filter cached version, filters run at display time. $info->content = format_module_intro('questionnaire', $questionnaire, $coursemodule->id, false); }

and it works like expected.