How to send KDE5 desktop notification from a bash script?

On my install of Kubuntu 15.10 and KDE neon, notify-send command was not available until I installed the libnotify-bin package.

After installing libnotify-bin, notify-send works fine:

sudo apt-get install libnotify-bin

At least first two options should work, I just have a problem with notifications in KDE in general: https://bugs.launchpad.net/ubuntu/+source/kde-runtime/+bug/1547752

notify-send 'text'
kdialog --passivepopup 'text' 5

first 'notify-send' did not work for me. But when I enabled 'notifications' widget (/icon or whatever) in Tray, it worked.

Try enabling the Tray notifications applet.