tps.xsl

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:xd="http://www.oxygenxml.com/ns/doc/xsl"
    exclude-result-prefixes="xs xd"
    version="1.0">

    <xsl:template match="trabalhos">
        <table border="1">
            <xsl:apply-templates/>
        </table>
    </xsl:template>

    <xsl:template match="grupo">
        <tr>
            <td>
                Grupo <xsl:number/>
            </td>
            <td>
                <table>
                    <xsl:apply-templates select="aluno1|aluno2|aluno3"/>
                </table>
            </td>
        </tr>
    </xsl:template>

    <xsl:template match="aluno1|aluno2|aluno3">
        <tr>
            <td>
                <xsl:value-of select="."/>
            </td>
        </tr>
    </xsl:template>

</xsl:stylesheet>