Usage

The XDG method: Create an emacsclient.desktop file that handles the x-scheme-handler/org-protocol MIME type:

[Desktop Entry]
Name=Emacs Client
Exec=emacsclient %u
Icon=emacs-icon
Type=Application
Terminal=false
MimeType=x-scheme-handler/org-protocol;
(Note the MimeType= line above, which is for org-protocol: URIs.)

Put the file in ~/.local/share/applications or /usr/local/share/applications.

You might have to open the file ~/.local/share/applications/mimeapps.list and add a line like this:

x-scheme-handler/org-protocol=emacsclient.desktop
Add that under the [Default Applications] section.

You can also achieve the last step via xdg-mime default emacsclient.desktop x-scheme-handler/org-protocol, which is probably the more official way to do it. –

Use zotilo to copy the ID of items to clipboard (can be put on context menu in zotero, or done via shortcut)

Further reference: https://forums.zotero.org/discussion/66778/zotero-select-items-does-not-work-anymore