Follow these steps:
Kubuntu 16.10 replaces the old screen shot tool KSnapshot with Spectacle but does not change the keyboard setting accordingly. Under System Settings -> Shortcuts -> Custom Shortcuts the folder “Screenshots” must be developed to show an entry “Start Screenshot Tool”. The trigger for this entry must be set to be the print screen key. A dialog will prompt warning that the key is already assigned; it is assigned to KSnapshot; therefore ignore the warning.