For Page Level Tracing specify the Page Directive as
<%@ Page Trace="true" %>
You can view the page on which trace is enabled to true to see the details.
For Application Level Tracing modify web.config as:
<configuration>
<system.web>
<trace enabled="true" requestLimit="10" pageOutput="false" traceMode="SortByTime" localOnly="true" />
</system.web>
</configuration>
You can view the Trace at http://<server>/<webApplicationName>/trace.axd
Trace messages View in ASP.NET
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