Why do you want to access to that instead of creating your own VPN? Can you clarify? If I understand what you are trying to do. I don’t think is possible to directly read the com.apple.vpn.managed.applayer type payload in an iOS app using the WireGuard protocol. Apple's VPN configuration system should restricts access to this specific payload type for security reasons, limiting it to system-level VPN frameworks and profiles, otherwise could be a security issue.
If you need to manage VPN configurations programmatically in your iOS app, you might want to consider using Apple's Configuration Profiles framework, which allows you to install and manage VPN profiles.
https://developer.apple.com/documentation/devicemanagement/applayervpn
Albert Pascual
Worldwide Developer Relations.