Will this suffice?

DECLARE @XML XML = '<root><Books><Book><ID>2</ID><Name>Sql Server Admin</Name>

<Author><Name>Joseph</Name><Age>35</Age></Author></Book></Books></root>' ;

SELECT @XML.query('/root/Books/Book/Author') ;

If not, you'll need to query the values within the Author node, and then recompose it into XML with a FOR XML clause.

DECLARE @XML XML = '<root><Books><Book><ID>2</ID><Name>Sql Server Admin</Name>

<Author><Name>Joseph</Name><Age>35</Age></Author></Book></Books></root>' ;

SELECT

@XML.value('(/root/Books/Book/Author/Name/text())[1]','varchar(100)') AS Name,

@XML.value('(/root/Books/Book/Author/Age/text())[1]','varchar(100)') AS Age

FOR XML PATH('') ;