By right-clicking on the KNotes icon in the system tray you get a help menu, but it does not contain anything.
I confirm it
Git commit f245faae1ff603227fad8c4679698fdfb4261d87 by Laurent Montel. Committed on 24/12/2018 at 13:06. Pushed by mlaurent into branch 'Applications/18.12'. Fix Bug 402453 - KNotes help menu is empty FIXED-IN: 5.10.1 M +36 -4 src/apps/knotesapp.cpp https://commits.kde.org/knotes/f245faae1ff603227fad8c4679698fdfb4261d87