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, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://docs.sitefinity.com/for-developers-query-comments

GetCommentByKeySnippet.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Telerik.Sitefinity.Services;
using Telerik.Sitefinity.Services.Comments;

namespace Telerik.Sitefinity.Documentation.CodeSnippets.DevGuide.SitefinityEssentials.Modules.Comments
{
    public partial class GetCommentByKeySnippet
    {
        public static IComment GetCommentByKey(string commentKey)
        {
            // Gets an instance of the comments service
            var cs = SystemManager.GetCommentsService();

            //instantiate comment filter
            var commentFilter = new CommentFilter();
            commentFilter.CommentKey.Add(commentKey);

            //get the comment with the specified commentKey
            var comment = cs.GetComments(commentFilter).SingleOrDefault();

            return comment;
        }
    }
}