Items that are orphaned (i.e., not connected to any items in your Zotero database) will not have an “Open in My Library” button.

In the Add Citation box, you can click on the bubble for a cited item and then click “Open in My Library” (or another library name) to view the item in Zotero. Press Enter again to insert the citation and close the Add Citation box. The item will appear in the dialog box in a shaded bubble. Select an item by clicking on it or by pressing Enter when it is highlighted. Items you have already cited in the document will be shown at the top of the list under “Cited”. Matching items will be shown for each library in your Zotero database (My Library and any groups you are part of). Matching items will instantly appear below the dialog box. Start typing part of a title, the last names of one or more authors, and/or a year in the dialog box. The citation dialog is used to select items from your Zotero library and create a citation. You can begin citing by clicking the (“Add/Edit Zotero Citation”) button in the Google Docs toolbar or by selecting “Add/Edit Citation” from the Zotero menu, both of which will bring up the citation dialog.

Endnote generator for google docs