Can anybody give me a clue how to sort the rows by the nomen column
number 1?

It would have been a bit easier if you'd given a short sample
of the XML source, but I'll try anyway:

    <fo:table-body>
        <xsl:apply-templates/>
     </fo:table-body>

You probably want
     <fo:table-body>
        <xsl:apply-templates select="supply">
          <xsl:sort select="nomen"/>
        </xsl:apply-templates>
     </fo:table-body>