I want to quick add some plasmoid to desktop using keyboard shortcut, how to achieve this?

At this point it is not possible to add an applet through a keyboard shortcut unfortunately. You can write a Plasma script however to perform the applet addition and configure it by default.

bcooksley wrote:You can write a Plasma script however to perform the applet addition and configure it by default.

Can you give me some hints how to do that, some link mayby

Is there a way to quickly duplicate currently open plasmoid?

In theory, you could duplicate an already running applet. See http://techbase.kde.org/KDE_System_Admi ... pScripting for more information. Unfortunately you cannot directly trigger a script to run via another script - but you could trigger the scripting console to open with the script preloaded (at which point you would just have to run it).