In TYPO3-7.6 + the whole TypoScript for an extension can be retrieved with
$typoScript = $this->configurationManager->getConfiguration( $this->configurationManager::CONFIGURATION_TYPE_FRAMEWORK);
where for the 1st parameter exist 3 different options:
$this->configurationManager::CONFIGURATION_TYPE_SETTINGS
$this->configurationManager::CONFIGURATION_TYPE_FRAMEWORK
$this->configurationManager::CONFIGURATION_TYPE_FULL_TYPOSCRIPT
optional for the function $this->configurationManager->getConfiguration()
the extension-key can be given as 2nd parameter and the plugin-name as 3rd parameter. So the whole command looks like this:
$typoScript = $this->configurationManager->getConfiguration( $this->configurationManager::CONFIGURATION_TYPE_FRAMEWORK, $extensionKey, $pluginName );
Consider that the static template has to be included in the backend-template to return the desired output.
ConfigurationManager is an instance of
TYPO3\CMS\Extbase\Configuration\ConfigurationManager