I’m often using the following xsl template script to check the available values and items which are available for the Content Query Web Part.
This script can be added to the itemstyle.xsl for use. I’m always copying it from older projects, so now it’s on my blog for faster access 
<xsl:template name=”TestView” match=”Row[@Style='TestView']” mode=”itemstyle”>
<xsl:for-each select=”@*”>
ITEM:
<xsl:value-of select=”name()” />
VALUE:
<xsl:value-of select=”.” />
<BR />
</xsl:for-each>
<BR />
<BR />
</xsl:template>
<xsl:for-each select=”@*”>
ITEM:
<xsl:value-of select=”name()” />
VALUE:
<xsl:value-of select=”.” />
<BR />
</xsl:for-each>
<BR />
<BR />
</xsl:template>