192.0.2.1 in wildcard domain? Do I need to enter the same or something else to route all the wildcard domains requests to my cloudflare worker?
192.0.2.1 which is an IP address that routes nowhere and is safe to use as a fake origin to put an originless worker on top ofapi.example.com also goes to worker bound to *.example.com. 

john.doe@google.example.com), and then point the MX for google.example.com to Google, and then make the Email Worker forward (e.g. from whatever@example.com) to john.doe@google.example.com.
john.doe@google.example.comjohn.doe@google.example.comgoogle.example.comwhatever@example.com