Original layout for ContentBlock widget is:
<%@ Control Language="C#" %>
<%@ Register TagPrefix="sf" Namespace="Telerik.Sitefinity.Web.UI.PublicControls.BrowseAndEdit"
Assembly="Telerik.Sitefinity" %>
<
asp:Literal
ID
=
"contentHtml"
runat
=
"server"
></
asp:Literal
>
<
sf:BrowseAndEditToolbar
ID
=
"browseAndEditToolbar"
runat
=
"server"
Mode
=
"Edit"
Visible
=
"false"
>
</
sf:BrowseAndEditToolbar
>
<
asp:PlaceHolder
ID
=
"socialShareContainer"
runat
=
"server"
></
asp:PlaceHolder
>
You can easily find all default templates in Telerik.Sitefinity.Resources.dll. You can decompile Telerik.Sitefinity.Resources.dll and receive all necessary layouts.
When you will create copy and tweak it, you need to specify location to new layout in Advanced Settings of Content Block widget