configuration is returning 0 value

This really has no context, this really leads alot more detail to even look at.  Please post more information as to what you are doing

In over side has Setting Functionality inside setting we have few tabs like Basic option, Advance, Email, Notification etc. 

Under Advance we are rendering "Content Editor" list using 

#foreach($editor in $core_v2_configuration.Editors)
#beforeall
<select role="listbox" class="arrow" id="$core_v2_widget.UniqueId('EditorList')" name="$core_v2_widget.UniqueId('EditorList')">
#each
<option value="$editor.Value"#if ($editor.Value == $user.EditorType) selected="selected"#end>$editor.Name</option>
#afterall
</select>

Note:"$core_v2_configuration.Editors" is not returning the list. But in you documentation has property like below

It should return the Collection list.

Please suggest now, how it will work on my 12.x version..

In over side has Setting Functionality inside setting we have few tabs like Basic option, Advance, Email, Notification etc. 

Under Advance we are rendering "Content Editor" list using 

#foreach($editor in $core_v2_configuration.Editors)
#beforeall
<select role="listbox" class="arrow" id="$core_v2_widget.UniqueId('EditorList')" name="$core_v2_widget.UniqueId('EditorList')">
#each
<option value="$editor.Value"#if ($editor.Value == $user.EditorType) selected="selected"#end>$editor.Name</option>
#afterall
</select>

Note:"$core_v2_configuration.Editors" is not returning the list. But in you documentation has property like below

It should return the Collection list.

Please suggest now, how it will work on my 12.x version..

$core_v2_configuration.Editors has been marked obsolete in version 12.  Editors are no longer selectable and the method will always return an empty list.  I have filed a bug to review the documentation and ensure that obsolete methods are reflected correctly in the documentation.