Before the Bell: Knight Falls, Too Rises  NEW YORK (Reuters) - Knight Trading Group Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=NITE.O target=/stocks/quickinfo/fullquote"&gt;NITE.O&lt;/A&gt;  shares fell more than 6 percent before the bell on Wednesday  after the Nasdaq stock trader warned of a quarterly loss  because of weak stock trading volume.