I'm not 100% sure what you're asking, because your first example looks
correct, but your description sounds as if you might be looking for
something different. You access the value of a paramater using the same
syntax as for a variable. So for example, you could call

<xsl:apply-templates select="../TABLE[@id='Table_24C' and
DBNR=$CURRENT_DBNR]/>

(Assuming of course that you are looking for all TABLE elements that
are siblings of the current element, and have an attribute called id
with the value 'Table_24C' and a child element called DBNR with the
value of CURRENT_DBNR.)

However, if your parameter is defined in the actual template (ie it
isn't a global parameter defined at the top of your xsl stylesheet)
this is how you call the template:

      <xsl:apply-templates select="Table">
          <xsl:with-param name="CURRENT_DBNR" select="DBNR"/>
      </xsl:apply-templates>

Googling "xsl:param" or "xsl:with-param" will give you more general
information about parameters in xslt, but I hope this helps in the
meantime.