On my KDE install I disabled Nepomuk as it doesnt offer me any functionality.

  1. Disable Nepomuk System Settings -> Desktop Search -> Basic Settings, unticked Nepomuk and Strigi

This turned off Nepomuk, however I still got following notifications:

Nepomuk Indexing Disabled
Nepomuk Indexing Agnets Have Been Disabled
The Nepomuk service is not available or fully operational and attempts to rectify this have failed. Theref...

The following problems were detected:

- Nepomuk not running.

Additional help can be found here:

Googling around I found a forum thread that suggested to disable notifactions of the task bar calendar.

right clicking the clock -> settings -> calendar -> disable here the “show events” checkbox

Will see if it helps