@syntax Routers cannot see DNS requests (maybe some can, mine cant) which your smartmeter may request, but you can set your smartmeter to use your Linux machine as DNS proxy and log DNS queries. This can be done using dnscrypt-proxy package, you can enable logging with https://github.com/DNSCrypt/dnscrypt-proxy/wiki/Logging
and if your smartmeter sends some requests you will be able to see them by filtering logs with smartmeter IP address.