How do I find the address or file server to my time machine back up

If your backup was to a time capsule.. simply open Airport Utility on your computer where the backups were originating. Click the icon of the Time Capsule and.. there .. lo and behold.. the IP address.

If your backup was to a NAS or any other server on the network, simply check the DHCP list from your main router.. or ping it by name from your computer using terminal.