> <xsl:when test="@requiredknowledge= 
> number(preceding::chunk_name1_knowledge) "> 
> 
> The problem now that I want to iterate the <xsl:when>
> condition because I have got in the xml resource
> chunk_name1_knowledge, chunk_name2_knowledge, 
> chunk_name3_knowledge, 
> chunk_name4_knowledge, etc.
>  

It's bad XML design to use structured element names in this way. That's what
attributes are for:

<chunk_name_knowledge nr="1">

But if you can't change the XML, you can use 

preceding::*[local-name()=concat('chunk_name', $n, '_knowledge')]

Don't expect it to be fast.

Michael Kay
http://www.saxonica.com/