If you searched using a desktop browser, check your browser history.
If you added the item to your Watch List, check your list -- both active and ended items.
Check your Recently Viewed list to see the last hundred or so items you viewed since the last time you cleared your list:
https://www.ebay.com/mye/myebay/rvi
If you performed a general search (as opposed to an Advanced Search, or a search using the eBay app), go to ebay.com and try entering the first keyword you might have used to see what searches are suggested.
If you searched using the Advanced Search page, your browser may remember your recent search keywords. Click on the search field on that page or enter the first few letters of your search keywords.
If you searched using the eBay app, you can see recent searches under the Saved menu -- the same way you reach your Saved Searches or Saved Sellers.
