Judy, you should be able to get a good idea but might not be exact. If you go to your traffic sources, click on Google Product Listing Ads. Find your list of listings that came up as a result, then click on one of the listing. It will take you to the specific stat for that listing. Keyword should show up, if any. My best guess is that it is likely the keyword listed there. I think if you go too far back, you won't be able to click on the listing to get a hint. Worth checking out! But yes, would be nice to know the keyword used from that source as you said.