The Google documentation has a tutorial example of a simple
addressbook:
https://developers.google.com/protocol-buffers/docs/tutorials
The Prolog equivalent is in
/usr/lib/swi-prolog/oc/packages/examples/protobufs/interop/addressbook.pl
and you can run it by make run_addressbook, which will run protoc
to generate the _pb.pl files and then run the example. The
resulting file is addressbook.wire.