This message was posted on behalf of Intel Corporation
Thank you for reaching out. I would like to let you know that for all Ubuntu questions on Joule, you should contact the Ubuntu Support. Here’s the link https://developer.ubuntu.com/en/snappy/start/intel-joule/. Please keep in mind that this product is still in beta.
I came to realize that "xdk-daemon" has to be installed and running on the target device to be accessed from XDK. And I found an answere here;
The Intel XDK xdk-daemon is currently (November, 2016) only supported on the Yocto and Ostro Linux distributions. Work is ongoing to provide a version of the xdk-daemon that will run on a wider range of IoT Linux platforms.
It appears that xdk-daemon setups port forwarding from tcp input to 58888. I hope they do it first for Ubuntu. Until then I will have to wait or use another IDE.