I'm using this URL to implement the App authenticity for iOS. https://developer.ibm.com/mobilefirstplatform/documentation/getting-started-6-3/authentication-security/application-authenticity-protection/application-authenticity-protection-native-ios/
However, I need to know where to find the worklight.plist to make sure that the applicationId is matching what i'm putting in the application-descriptor.xml.
The worklight.plist file is available only after building the MobileFirst application using the MobileFirst Studio Eclipse plug-in (or CLI commandline tool).
For Hybrid applications,
You can then find the worklight.plist file in the your-project\apps\your-app\iphone\native folder.
For Native applications,
You need to only generate the NativeAPI for iOS and it'll be located in the generated folder, in your-project\apps\your-nativeapi\WorklightAPI folder. You then need to follow the native apps tutorial to copy over this (and more) files to the Xcode project.