How to open "Trash" through terminal?

The trash folder should be located under:

/home/your_username/.local/share/Trash

So you should be able to access it via:

cd ~/.local/share/Trash

The folder might not exist unless you delete something from the filesystem. In this case you would run into an error (saying that the folder does not exist).

If you want to open Trash using Nautilus run the following:

nautilus trash://

For Ubuntu 18.04 and newer, use gio. For older versions, use gvfs-ls and gvfs-trash.

To read the trash:

gio list trash://
gvfs-ls trash://

To send files or directories to the trash:

gio trash [FILE or DIR]
gvfs-trash [FILE or DIR]

To empty it:

gio trash --empty
gvfs-trash --empty