End of the global menu section, upper left. I think it is there only if there have been photos deleted recently-- it can't be empty. If you don't see it, maybe you didn't really delete the photos?
For instance, if you select a picture and hit delete, it only deletes the photo from that album-- it doesn't remove it from the library or move it to "Recently Deleted." To delete a picture, you can select it and then hit command-delete. That will move the photo to "Recently Deleted."
And if you delete an album, it doesn't delete any photos at all-- just its internal list of the pictures that belonged in that album. You can select-all the pictures in the album and hit command-delete to move all those pictures to "Recently Deleted."