In the following transformation the name space URI will not appear in
the c:choose tag, since it is already present in it's parent tag
jsp:root.

<?xml version="1.0"?>
<xsl:stylesheet
       xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
       version="2.0">

       <jsp:root
               xmlns:jsp="http://java.sun.com/JSP/Page"
               xmlns:c="http://java.sun.com/jsp/jstl/core"
               version="2.0">
           <ul>
               <c:choose>
                   <c:when test="">Print Something</c:when>
                   <c:otherwise></c:otherwise>
               </c:choose>
           </ul>
       </jsp:root>

I think there are more challenges when it comes to transforming EL,
but since these questions pertain to JSP/JSTL - the JSTL mailing list
may know how to represent EL in XML syntax.

-Regards
Rashmi