We've created an ADF from an XSD. The Xsd contains namespaces. When we look at the adf in the datamapper it detects which namespace an element belongs to, it says "//ELEM! //NS=s" in the directives. When mapping to this element I expect the outdata to be like this:

< s:Verb >Add< /s:Verb >

But the namespace is missing, it creates the element as < Verb >Add< Verb >

How should I do to make it use the namespace in the element?

To add namespaces as prefix , we need to use literals.Literlas provides a way through which we can  add namespaces to output XML file.
1.) Create Literals on input side. suppose String1 and String 2
2.) Map String 1 with name/xmlAttr
3.) MapString2 with value/xmlAttr
4.) Map Envelop to xmlAttr
5.) Inside the link code of string1->name/xmlAttr, you nees to mention the source expression like "xmlns:s" as in your case which is      mentioned in your XSD file.
6.) In same way , mention the source expression for string2->value/xmlAttr like "urn:segments" which is according to the XSD file which      you are using. Source expression must be in double quotes.
This will show the output as described above in problem.