FrontendUser::getCookie() 

public function getCookie()
{
	$cookieName = $this->getCookieName();
	if ($request = &$GLOBALS['TYPO3_REQUEST']) {
		$cookieParams = $request->getCookieParams();
		if ($value = $cookieParams[$cookieName] ?? false) {
			return $value;
		}
	}
	if ($cookie = $_COOKIE[$cookieName] ?? false) {
		return $cookie;
	}
	if ($cookies = \nn\t3::Cookies()->getAll()) {
		return $cookies[$cookieName]['value'] ?? '';
	}
	return '';
}