right click on the root node in scene builder and then choose copy . and paste it in any text editor.
out put :
<Group id="sb-clipboard" xmlns:fx="http://javafx.com/fxml">
<fx:define>
<AnchorPane id="AnchorPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0">
<children>
<Button id="button1" layoutX="140.0" layoutY="104.0" mnemonicParsing="false" text="Button" />
<RadioButton id="radioButton1" layoutX="283.0" layoutY="172.0" mnemonicParsing="false" text="RadioButton" />
<ToggleButton id="toggleButton1" layoutX="94.0" layoutY="234.0" mnemonicParsing="false" text="ToggleButton" />
</children>
</AnchorPane>
</fx:define>
</Group>