I follow these steps to disable Nepomuk:
- Go to System Settings --> Workspace Appearance and Behavior --> Desktop Search
- Untick "Enable Strigi Desktop File Indexer" and "Enable Nepomuk Semantic Desktop" under Basic Setting Tab
- Choose "Ignore all removable media" on Removable media handling and also make sure all folders are left unticked in "Customize index folders ..." under Desktop Query Tab
- Select "Disable Automatic Backups" on Backup frequency under Backup Tab
- Go to System Settings --> Common Appearance and Behavior --> Application and System Notifications --> Manage Notifications
- Under Applications Tab, select "Desktop Search" on Event source and make sure all states are empty
- Do the same for "Nepomuk file watch service" and "Semantic Desktop" on Event source
- Quit System Settings
For disabling Akonadi, open the terminal then enter the directory ~/.config/akonadi/akonadiserverrc and set the value of "StartServer" on [QMYSQL] to false.
[QMYSQL] ... StartServer=false
After finishing all steps described above, restart the KDE. Nepomuk and Akonadi have been disabled.
Note: I configure my System Settings to Classic Tree View (see picture below).