Before buying spark code, I want to confirm that can I use spark core without internet connection?
For example if I want to create a project where I send some code from android to core then core validates whether its correct or not and if it is, will blink an LED.
Like I said, if you like to use cloud functionalities on a local network, you can use the local cloud. Most functions from the public cloud are included and can be used.
You could print your IP address over Serial, or check your router for connected devices. I'm sure there are other ways as well.
To get the IP address you login to your router and see what it is, or configure your router so that it always gives the same IP address to your core (DHCP Reservation). You can also program your Core to print the IP address to the serial port.