Method 1: search for messages in the trash with a standard Gmail search: you just have to remember to look at the very bottom for the line: Deleted messages match your search. View them or go to Trash to delete forever.. Click on “View them” to see the messages in the Trash that match the search you’ve just entered.
Method 2: Simply search for in:trash and you’ll find that it shows you every message in the Trash on Gmail.
Method 3: A click on “More”, however, and there’s much more revealed:
Did you see “Trash” listed there? Click on it and Gmail actually does a search for “in:trash” and shows you the result, your trash folder.