Where is Finder Sync API Extension

You installed a third-party cloud data client such as "Google Drive" that integrates with the Finder, and it isn't working. Either remove it, update it, or refer to its developer for support.

Were you able to find out which cloud client (box, drive, dropbox, and onedrive) it was?

If that can help, I had a similar issue today and discovered it was coming from Google Drive by putting the mouse over the icon in the top bar. The icon of the mouse was changing for a spinning wheel when over it. The issue disappeared (so as the pop up windows requiring to FinderSyncAPIExtention) the minute I opened Chrome and login the web page of Google Drive with my credentials.

I have this problem too. I get the "where is..." window on startup and occasionally at other times. Google Drive also sometimes silently fails to sync a file, and will only correct the problem when it is quit and restarted. These problems suggest a delayed response from the MacOS when Google drive is asking MacOS for something. I may have found a fix for this:

Doyou have the "where is..." window or the intermittent silent sync failures from Google Drive? If so, are you also running the DropBox sync app? For me the answer is Yes. (I need both because of different groups I need to share with.) To check this issue I turned off the DropBox app (deselected the setting "start dropbox on restart). Then I restarted my mac. There was no "where is..." window this time. I'm hoping this will remain true. and maybe my sync problems will improve as well. What is your experience??

I believe I fixed this problem on my three macs running Lion and El Capitan MacOS's. I have accounts on both Google Drive and Dropbox. When I quit the Dropbox application, the Google Drive application began updating reliably. When I later noticed a file that didn't update, I discovered that the dropbox application had restarted. To prevent this I went in System Preferences>accounts>login items and removed Dropbox from the list of login items.

Find Google Drive APP in APP Folder, click,and click OK.. find Dialogue will disappear

This worked for me except I had to:

1. Go to Applications folder
2. Double click Google Drive app (this worked almost immediately. However...)
3. ...I also had to click Cancel to close the find dialog.