Kim is right in that DocuSign currently does not have good documentation for XML formatted request bodies. However sometimes JSON is not an option due to technical limitations, you don't want to re-write parsing code, or other reasons, and developers are stuck with XML format.
With that said, here is the proper XML format for the eventNotifications object, along with all the possible properties you can set on it:
<eventNotification>
<EnvelopeEvents>
<envelopeEvent>
<envelopeEventStatusCode>sample string 1</envelopeEventStatusCode>
<includeDocuments>sample string 2</includeDocuments>
</envelopeEvent>
<envelopeEvent>
<envelopeEventStatusCode>sample string 1</envelopeEventStatusCode>
<includeDocuments>sample string 2</includeDocuments>
</envelopeEvent>
</EnvelopeEvents>
<includeCertificateWithSoap>sample string 6</includeCertificateWithSoap>
<includeDocuments>sample string 8</includeDocuments>
<includeEnvelopeVoidReason>sample string 9</includeEnvelopeVoidReason>
<includeSenderAccountAsCustomField>sample string 11</includeSenderAccountAsCustomField>
<includeTimeZone>sample string 10</includeTimeZone>
<loggingEnabled>sample string 2</loggingEnabled>
<recipientEvents>
<recipientEvent>
<includeDocuments>sample string 2</includeDocuments>
<recipientEventStatusCode>sample string 1</recipientEventStatusCode>
</recipientEvent>
<recipientEvent>
<includeDocuments>sample string 2</includeDocuments>
<recipientEventStatusCode>sample string 1</recipientEventStatusCode>
</recipientEvent>
</recipientEvents>
<requireAcknowledgment>sample string 3</requireAcknowledgment>
<signMessageWithX509Cert>sample string 7</signMessageWithX509Cert>
<soapNameSpace>sample string 5</soapNameSpace>
<url>sample string 1</url>
<useSoapInterface>sample string 4</useSoapInterface>
</eventNotification>