SF_10.1, SF_10.2, SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3 - https://docs.sitefinity.com/tutorial-add-comments-widget-and-counter-in-a-widget-template

AddCommentsWidget.ascx

<%@ Control Language="C#" %>
<%@ Register Assembly="Telerik.Sitefinity" Namespace="Telerik.Sitefinity.Modules.Comments.Web.UI.Frontend" TagPrefix="comments" %>

<%-- Add Comments widget --%>

<comments:CommentsWidget runat="server"
               ThreadKey='<%# ControlUtilities.GetLocalizedKey((Guid)Eval("Id")) %>' 
               AllowComments='true' 
               ThreadTitle='<%# Eval("Title") %>' 
               ThreadType='<%# Container.DataItem.GetType().FullName %>' 
               GroupKey='<%# ControlUtilities.GetUniqueProviderKey("Telerik.Sitefinity.Modules.News.NewsManager", Eval("Provider.Name").ToString()) %>' />

<%-- Add Comments counter --%>

<comments:CommentsCountControl runat="server"
                ThreadKey='<%# ControlUtilities.GetLocalizedKey((Guid)Eval("Id")) %>' 
                NavigateUrl="#commentsWidget"
                AllowComments='<%# Eval("AllowComments") %>'
                DisplayMode="ShortText"
                ThreadType='<%# Container.DataItem.GetType().FullName %>'/>