Enable WCF Service Trace Logging - view with SvcTraceViwer.exe (i.e. C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.2 Tools)

app.config.xml

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <!-- ... -->
    <system.serviceModel>
        <!-- ... -->
        <diagnostics wmiProviderEnabled="true">
            <messageLogging logEntireMessage="true" logMalformedMessages="true" logMessagesAtServiceLevel="true" logMessagesAtTransportLevel="true" maxMessagesToLog="3000" />
        </diagnostics>
    </system.serviceModel>
    <!-- ... -->
    <system.diagnostics>
        <sources>
            <source name="System.ServiceModel" switchValue="Information, ActivityTracing" propagateActivity="true">
                <listeners>
                    <add name="xml"/>
                </listeners>
            </source>
            <source name="System.ServiceModel.MessageLogging">
                <listeners>
                    <add name="xml"/>
                </listeners>
            </source>
            <source name="myUserTraceSource" switchValue="Information, ActivityTracing">
                <listeners>
                    <add name="xml"/>
                </listeners>
            </source>
        </sources>
        <sharedListeners>
            <add name="xml" type="System.Diagnostics.XmlWriterTraceListener" initializeData="C:\logs\Traces.svclog" />
        </sharedListeners>
    </system.diagnostics>
</configuration>

Thank you. The <system.serviceModel><diagnostics><messageLogging> element is inexplicably not mentioned by the official documentation, and it's a nasty gotcha.