Hi,

I are trying to get sObject name corresponding to selected CDC entity from PlatformEventChannelMember::fullName when getting response for MetadataAPI::listMetadata call.

Refer below link to know more about fullname.
https://developer.salesforce.com/docs/atlas.en-us.232.0.api_meta.meta/api_meta/metadata.htm

For custom sobject as CDC selected entity we get fullName like : ChangeEvents_<CUSTOM_SOBJECT_NAME>_ChangeEvent
Ex : <fullName>ChangeEvents_Patient_ChangeEvent</fullName>

For standard sobject as CDC selected entity we get fullName like : ChangeEvents_<STANDARD_SOBJECT_NAME>ChangeEvent
Ex : <fullName>ChangeEvents_AccountChangeEvent</fullName> fullName returned from listMetadata (soap based api) of MetadataAPI for type PlatformEventChannelMember does not start with ChangeEvents_ instead starts with CM_. And fullName also not ends with  ChangeEvent for User (standard sobject).

For User (standard sobject) as selected entities, I am getting fullName like : <fullName>CM_ChangeEvents_User</fullName>
This is causing issue to me since fullName does not start with ChangeEvents_ but starts with CM_ and also not ends with  ChangeEvent

MY QUERIES:
1. What does "CM_" mean in prefix of "User" entity fullName? Is this pattern expected ?
Refer below link to know more about fullname. 
https://developer.salesforce.com/docs/atlas.en-us.232.0.api_meta.meta/api_meta/metadata.htm

2. When getting response from MetadataAPI::listMetadata api call for type PlatformEventChannelMember, can fullName start with something like "CM_" for User (standard sobject) ?

3. Why fullName isn't ending with "ChangeEvent" for "User" entity which is a standard sObject?
Refer below link
https://developer.salesforce.com/docs/atlas.en-us.232.0.api_meta.meta/api_meta/meta_platformeventchannelmember.htm
for quick view  
{
"The change event name of an entity selected for Change
Data Capture notifications. For example, for the Account standard object, the
name is AccountChangeEvent, or for a custom object MyObject__c, the name is
MyObject__ChangeEvent"
}