When I save something in a variable in a loop for-each i dont have access to
this variable out of the loop for-each.

<xsl:for-each select="Attribute_Groups/Attribute">
	<xsl:variable name="aname" select="@Name" />
	........
</xsl:for-each>

How can i access the variable aname out of the loop for-each?

You can't. The scope of a variable is the element where it was
declared. Your problem is that you want to program XSLT the same
way you'd do it in, say, JavaScript. If you give a description
of the original problem someone will show you a XSLT solution.