/etc/xdg/autostart/xembedsniproxy.desktop is in plasma-systray-legacy 0~git20151104-ded1538-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Exec=xembedsniproxy
Name=XembedSniProxy
Type=Application
X-KDE-StartupNotify=false
OnlyShowIn=KDE;
X-KDE-autostart-phase=0
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