I need a global menu in kde how can I get this.
In KDE4, the appmenu was nice and easy. See here.
In Plasma 5, however, this was discontinued. The reason is that
appmenu made use of
dbusmenu which has been deprecated by Canonical. Gnome now uses a new standard,
Maybe you should have researched a bit more: the above are the first pages that Google shows when searching "appmenu qt plasma5".
While it was true in the past this wasn't ported. It is now working in the staging version of KDE, version 5.9. You can read more about it here.
If you have KDE backports ppa or KDE Neon you should eventually get this version.
You can add those ppa's easily like this.
sudo add-apt-repository ppa:kubuntu-ppa/backports sudo apt-get update
If you want to add the source yourself check out the launchpad. https://launchpad.net/~kubuntu-ppa/+archive/ubuntu/backports