where is Trash folder in Mac ?

If you click on the Trash icon in the Dock it will open the Trash Folder. The folder is located at…

~/.Trash

It's normally invisible so you would need to press "command shift ." to see it.

Usually Trash icon is located in your dock (right side).

You shouldn't be able to delete the Trash folder from your Dock. To put it back, you may reset your Dock settings:

1. Open Terminal (/Applications/Utilities/Terminal.app)
2. Run the following command to delete the Dock preferences file:

rm ~/Library/Preferences/com.apple.dock.plist

Log out and back in.

The Ptaxey recommendation should work.

Or:

apple->ForceQuit->Finder to reset to "normal".

FWIW, If your question is how do I add the Trash icon to the sidebar, you can't.