In some forums I found solutions like this:
Seems like the "Cordova" folder isn't getting copied into the project during cordova platform add ios So, you'll have to copy the "Cordova" source folder into your project manually. But you'll have to download the ios source packages from github first, which is located at:
After downloading the "cordova-ios-master.zip" package and unzipping it, copy the folder named "CordovaLib" into your project next to the Xcode project file:
PROJECT_FOLDER/platforms/ios/CordovaLib <------- here
But it does not work...