How to improve performance of this linq query ?

var results = from myRow in dtTaskandBugs.AsParallel()
              select myRow;
results.ForAll(r =>
  {
    r["Storyid"] = GetStoryid(r["Id"]);
    r["FeatureID"] = Fidname(r["Storyid"]);
    r["FeatureName"] = r["FeatureID"].ToString() == "0" ? 
      "Anonymous" : 
      fname(r["FeatureID"]);
  });

PLINQ could help if performance is an issue. It actually determines whether it expects a speed-up by running the query in parallel and will run parallel or sequentially accordingly.

If you have control over the GetStoryid(), Fidname(), or fname() functions you could use async/await. If they have heavy delay (e.g. accessing another DB or something) this might help:

public async Task<int> GetStoryid(int id)
{
  Task<int> processing = Task.Run(() => { /*delay-heavy processing*/});
  //Any independent processing
  int result = await processing;
  //Processing dependent on the result
  return result;
}
//Same basic idea for Fidname() and fname()

var results = from myRow in dtTaskandBugs.AsParallel()
              select myRow;
results.ForAll(async r =>
  {
    Task<int> storyProcessing = GetStoryid(r["Id"]);
    Task<int> fidProcessing = Fidname(r["Storyid"]);
    Task<string> featureProcessing = r["FeatureID"].ToString() == "0" ? 
      Task.FromResult("Anonymous") : 
      fname(r["FeatureID"]);
    r["Storyid"] = await storyProcessing;
    r["FeatureID"] = await fidProcessing;
    r["FeatureName"] = await featureProcessing;
  });

EDIT: original edit deleted for space.
EDIT2: So after reading more into Query and seeing below that PLINQ isn't helping, I'm guessing the DB calls are your biggest problem. The code below demonstrates a working example of what my suggestion would be (async) along with comments to help you to get it to work:

class Program
{
    private static Random randomNumber = new Random();

    static void Main(string[] args)
    {
        int tableRows = 10;
        List<Dictionary<string, int>> table = new List<Dictionary<string, int>>();
        for (int i = 0; i < tableRows; i++)
        {
            Dictionary<string, int> row = new Dictionary<string, int>();
            row.Add("Id", i);
            row.Add("StoryId", tableRows + i);
            row.Add("FeatureId", tableRows * 2 + i);
            table.Add(row);
        }

        var results = from myRow in table
                      select myRow;
        List<Task> tasks = new List<Task>();
        foreach (var result in results)
            tasks.Add(Process(result));
        Task.WaitAll(tasks.ToArray()); //this is a blocking operation to wait on
                                       //all tasks to complete
        Console.ReadKey();
    }

    public static async Task Process(Dictionary<string, int> row)
    {
        Task<int> storyProcessing = GetStoryid(row["StoryId"]);
        Task<int> fidProcessing = Fidname(row["FeatureId"]);
        Task<string> nameProcessing = fname(row["Id"]);
        await Task.WhenAll(storyProcessing, fidProcessing, nameProcessing);
        //---------
        Console.WriteLine($"#{row["Id"]} complete. SID: {storyProcessing.Result}, FID: {fidProcessing.Result}, FN: {nameProcessing.Result}");
        /*---------
         * Replace above with something like:
         * row["StoryId"] = storyProcessing.Result;
         * row["FeatureId"] = fidProcessing.Result;
         * row["Id"] = nameProcessing.Result;
         */
    }

    public static async Task<int> GetStoryid(int id)
    {
        //---------
        await Task.Delay(randomNumber.Next(10000));
        return id * 10;
        /*---------
         * Replace above with something like:
         * string _wiql = String.Format("SELECT [System.Id],[System.Title] " +
                           "FROM WorkItemLinks WHERE ([Source].[System.WorkItemType] = 'Product Backlog Item') " +
                           "And ([System.Links.LinkType] = 'System.LinkTypes.Hierarchy-Forward') And ([Target].[System.Id] = {0}  " +
                           "AND  [Target].[System.WorkItemType] = 'Task')" +
                           " ORDER BY [System.Id] mode(Recursive,ReturnMatchingChildren)", _TbId);
         * Query _query = new Query(_workitemstore, _wiql);
         * WorkItemLinkInfo[] links = await Task.Factory.FromAsync(_query.BeginLinkQuery, _query.EndLinkQuery);
         * if (links.Count() == 2)
         *     return links[1].SourceId;
         * return 0;
         */
    }
    public static async Task<int> Fidname(int id)
    {
        //---------
        await Task.Delay(randomNumber.Next(10000));
        return id * 10;
        /*---------
         * Replace above with something like:
         * string _wiql = String.Format("SELECT [System.Id],[System.Title],[System.Links.LinkType] FROM WorkItemLinks WHERE ([Source].[System.Id] = {0})" +
                          " And ([System.Links.LinkType] = 'System.LinkTypes.Hierarchy-Reverse')" +
                          " And ([Target].[System.WorkItemType] = 'Feature') ORDER BY [System.Id]", _id);
         * Query _query = new Query(_workitemstore, _wiql);
         * WorkItemLinkInfo[] links = await Task.Factory.FromAsync(_query.BeginLinkQuery, _query.EndLinkQuery);
         * if (links.Count() == 2)
         *     return links[1].TargetId;
         * return 0;
         */
    }
    public static async Task<string> fname(int id)
    {
        await Task.Delay(randomNumber.Next(10000));
        return $"{id * 10}";
        /*---------
         * Replace above with something like:
         * string Ftitle = "";
         * string _wiql = string.Format("SELECT[System.Title], [System.Id]" +
                              " FROM WorkItems WHERE[System.Id]  = {0}" +
                              "  AND[System.WorkItemType] = 'Feature' ORDERBY[Microsoft.VSTS.Common.Priority]", fid);
         * Query _query = new Query(_workitemstore, _wiql);
         * WorkItemCollection workItems = await Task.Factory.FromAsync(_query.BeginQuery, _query.EndQuery);
         * foreach (WorkItem workItem in workItems)
         *     Ftitle = workItem.Title;
         * return Ftitle;
         */
    }
}

More info: Task-based Asynchronous Programming (TAP)[^], APM to TAP[^], and Query[^].