For those interested in the solution:

I identified that the annoying sound notification file is
KDE_Chimes_2.ogg (from /opt/trinity/share/sounds/).

I have searched for it into my TDE settings:

   grep -rn KDE_Chimes_2.ogg ~/.trinity/share/config/

and found that *knotify.eventsrc* was the candidate!

Then, in knotify.eventsrc I changed all lines

   soundfile[$e]=<SOME_FILE>

to

   soundfile[$e]=

Finally, in order to mimic a TDE restart (and avoid to restart i3),
I closed/killed all TDE apps, including tdeinit and any related tde
services.

*Then I gave a try to kpdf and it stopped to play this stupid noise*.
(Sorry for its author.)

I can work again, peacefully!  I feel very very good because I love
kpdf-trinity and hate audio notifications!

Thanks for the help from many of you!
Nicolas

--
@Nik: tdeinit was already running under my i3 session (I guess it is run
by the first call to any TDE app I'm using among kpdf, konqueror,
amarok, kuickshow or ksnapshot).
FYI: my ~/.xinitrc is never sourced at X session startup.  My dm is gdm3
right now, but I fallback to xdm again.  I use gdm3 only because it is
graphically appealing and it sources /etc/profile... something that xdm
and lightdm do not by default.

On 16/11/2018 17:43, Nicolas Bercher wrote:
> Hi,
> 
> I'm currently using some Trinity apps (kpdf, amarok, ksnapshot,
> konqueror) into another window manager (wmii, then i3).
> Since I stopped using Trinity as my main desktop years ago (I changed
> machine and reinstalled Debian without Trinity) I'm only using the
> aforementioned packages.
> 
> Now, *applications such as kpdf and konqueror cannot be configured*
> anymore, or only partly.
> 
> Through years, I've already spent a lot of time trying to find a package
> for the missing configuration tools & config files for the event sounds 
> without success for the following:
> 
> * Things don't know how to configure:
> kpdf:
>  �- Where should I tell it not to emit any event sound?
> 
> konqueror:
>  �- Basic preferences like "View Mode" (tree view, etc.)
>  �- Menu Settings / Configure Konqueror : I got an empty window
>  �- Where should I tell it not to emit any event sound?
> 
> * Things can configure:
> kpdf:
>  �- Keyboard shorcuts: ~/.trinity/share/apps/kpdfpart/part.rc
> 
> konqueror:
>  �- Bookmarks
> 
> amarok & ksnapshot: all seems OK.
> 
> Nicolas
> 
> -- 
> PS: I have the following packages installed (deps excluded):
> 
> $ aptitude search '!~M~i~n-trinity$' -F "%p"
> amarok-common-trinity
> amarok-engine-xine-trinity
> amarok-trinity
> digikam-trinity
> k3b-trinity
> kamera-trinity
> kasteroids-trinity
> katomic-trinity
> kbackgammon-trinity
> kbattleship-trinity
> kblackbox-trinity
> kbounce-trinity
> kcoloredit-trinity
> kcontrol-trinity
> kde-systemsettings-trinity
> kdebase-data-trinity
> kdebase-kio-plugins-trinity
> kdegames-card-data-trinity
> kdegames-trinity
> kdelibs-data-trinity
> kdelibs4c2a-trinity
> kdemultimedia-kio-plugins-trinity
> kdesktop-trinity
> kdm-trinity
> kenolaba-trinity
> kfind-trinity
> kfouleggs-trinity
> kghostview-trinity
> kgoldrunner-trinity
> kicker-trinity
> kjumpingcube-trinity
> klickety-trinity
> klines-trinity
> kmag-trinity
> kmahjongg-trinity
> kmines-trinity
> kmix-trinity
> knetwalk-trinity
> kolf-trinity
> kolourpaint-trinity
> konq-plugins-trinity
> konqueror-nsplugins-trinity
> konqueror-trinity
> konquest-trinity
> kpat-trinity
> kpdf-trinity
> kpoker-trinity
> kreversi-trinity
> ksame-trinity
> kshisen-trinity
> ksirtet-trinity
> ksmiletris-trinity
> ksnake-trinity
> ksnapshot-trinity
> ksokoban-trinity
> kspaceduel-trinity
> ktron-trinity
> ktuberling-trinity
> kuickshow-trinity
> kwin4-trinity
> python-dcop-trinity
> tde-core-trinity
> tdeadmin-trinity
> tdebase-data-trinity
> tdebase-runtime-data-common-trinity
> tdebase-tdeio-plugins-trinity
> tdebase-tdeio-smb-trinity
> tdebase-trinity
> tdm-trinity