The CEP Matcher tab lets you easily view some current pings of any ping type. To access it, follow these first few directions for accessing the CEP. Once there, click on the "Matcher" tab. The message-matcher is set by default to TRUE, meaning all pings will be matched. Click "Run Matcher" and a few pings will show up.

Changing the message matcher will filter down the accepted pings, letting you hone in on a certain type. Generally, you can filter on any fields in a ping. For example, docType:

Fields[docType] == "main"

Or OS:

Fields[os] == "Android"

We can also combine matchers together:

Fields[docType] == "core" && Fields[os] == "Android" && Fields[appName] == "Focus"

Note that most of the time, you want just proper telemetry pings, so include this in your matcher:

Type == "telemetry"

Which would get us a sample of Focus Android core pings.

The Message Matcher documentation has more information on the syntax.

To see the available fields that you can filter on for any docType, see this document. For example, look under the telemetry top-level field at system-addon-deployment-diagnostics. The available fields to filter on are:

required binary Logger;
required fixed_len_byte_array(16) Uuid;
optional int32 Pid;
optional int32 Severity;
optional binary EnvVersion;
required binary Hostname;
required int64 Timestamp;
optional binary Payload;
required binary Type;
required group Fields {
    required binary submission;
    required binary Date;
    required binary appUpdateChannel;
    required double sourceVersion;
    required binary documentId;
    required binary docType;
    required binary os;
    optional binary environment.addons;
    optional binary DNT;
    required binary environment.partner;
    required binary sourceName;
    required binary appVendor;
    required binary environment.profile;
    required binary environment.settings;
    required binary normalizedChannel;
    required double sampleId;
    required binary Host;
    required binary geoCountry;
    required binary geoCity;
    required boolean telemetryEnabled;
    required double creationTimestamp;
    required binary appVersion;
    required binary appBuildId;
    required binary environment.system;
    required binary environment.build;
    required binary clientId;
    required binary submissionDate;
    required binary appName;
}

So, for example, you could have a message matcher like:

Type == "telemetry" && Fields[geoCountry] == "US"