Adding a cite tag within the blockquote tag using redactor's WYSIWYG?
You can use the Redactor Inline Styles add-on then use the following in your Redactor json config:

"plugins": ["source","fullscreen","inlinestyles"],
    "buttonsAddAfter": "italic",
    "buttonsAdd": {
        "cite": {
            "title": "Cite",
            "args": ["cite"]
        }
    }


You'll then be able to add a cite element within a blockquote formatted text.