That's sort of not what you want to do. With SOAP calls, you just follow the XML they provided in the documentation (https://www.regonline.com/api/default.asmx?op=GetEvent).
So in the particular case, you want to replace the CSSAVECONTENT
variable soapBody
to below:
<cfsavecontent variable="soapBody">
<cfoutput>
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Header>
<TokenHeader xmlns="http://www.regonline.com/api">
<APIToken>#apiToken#</APIToken>
</TokenHeader>
</soap:Header>
<soap:Body>
<GetEvent xmlns="http://www.regonline.com/api">
<eventID>#eventID#</eventID>
</GetEvent>
</soap:Body>
</soap:Envelope>
</cfoutput>
</cfsavecontent>
See what that returns for you.