How can add to the right click menu the libreoffice choice (writer,calc, etc) like kubuntu ?
i want when i am in the desktop or inside one from my folder and use right click in the menu i can add one libreoffice writer or calc .

can give me terminal command ?
can help me with graphical way ?

help me for you attention!

Right-click from where, Dolphin or some of the program? Specifically which extension, or is LibreOffice not an option for any extension?

On every system that I have installed KDE Neon, the right-click menu was already set up for the LibreOffice applications. There are at least two places where you can add file associations.

From within Dolphin, right-click on the file, select Open With, then if the application you want is not on this menu, select Other Application... The LibreOffice applications will be under Office. Select the one you want. If you want it to remember this program, select the Remember application association for all files or type at the bottom of the dialog.

The other way to set associations is with System Settings, under Personalization, Applications (or type Applications in the Search... box at the top. Under Applications select Default Applications to bring up the File Associations. On the search box under "File Associations" type in the extension to want to configure with the period (e.g. ".doc"). The various options may appear. Select the one you are interested in (e.g. "msword"). On the upper right it will show the file name extensions (e.g. "*.doc"). And below will be the Application Preference Order. Select the Add... button and a similar dialog as with Dolphin Other Application... will appear. Again, the LibreOffice applications will be under Office. Select the one you want. If there is more than one program listed, the one listed first will be the default (immediately available under the right-click menu under Dolphin). You can move programs up and down with the Move Up and Move Down buttons. Click Apply when done.

Also, if you are referring to the items available under the Create New... submenu, those items should be provided by the libreoffice-kde5 package.