With Serial I could not see the output. I am using Dragino MS14-P with M32W. Console is compatible with Serial, so I replaced it and the output is visible to the Serial Monitor of Arduino IDE.
there was a problem with the curly brackets. Even when the whole string is tested on ssh at the Dragino, the curl had a problem with the curly brackets. -g parameter helped the curl process sends json data over GET to an external emoncms. This is the description of curl -g:

-g, --globoff

This option switches off the "URL globbing parser". When you set this option, you can specify URLs that contain the letters {}[] without having them being interpreted by curl itself. Note that these letters are not normal legal URL contents but they should be encoded according to the URI standard.
Merge pull request #1 from fantomas/master

Updating EmoncmsClient example