One way to do this is with
FrontEndTokenExecute["PrintDialog"]
which will bring up the print dialog window.
If you would like to "add" a button to do this, you may create a palette using
CreatePalette[Button["Print me", FrontEndTokenExecute["PrintDialog"]]]
which will create a button that will allow you to print the active notebook.
(truth in advertising - I confirmed this with printing as a PDF; I do not have access to a printer on my RPi)