The only place Ctrl-Home and Ctrl-end are documented AFAICT is in the [Scintilla](https://www.geany.org/manual/current/index.html#scintilla-keyboard-commands) keybindings. As the text says these are inherited from the Scintilla editing widget, they are not Geany keybindings.
So they cannot be set by Geany and do not show in the Keybindings preference dialog or `Help->Keyboard Shortcuts` list which only reflects those modifiable bindings.