Like the other examples it builds against installed libvws plus the examples' libvwsx, through the companion repository's build. It expects a message server on localhost port 8181, so start the server of Chapter 8, A Message Server first, then run the client:

$ ./client-message
client-message: reply content (20 bytes): hello in a vrtql_msg

The reply is the server's echo of the message that was sent.