const 
 sJSON = 'здесь JSON-строка';
var
 JSONParamsVal: TJSONValue;
 JSONArray: TJSONArray;
begin
  JSONParamsVal := TJSONObject.ParseJSONValue(sJSON).Get('result').Get('ad_parameters');

  if JSONParamsVal is TJSONArray then
    JSONArray := TJSONArray(JSONParamsVal);

...
...

 LData: TJSONArray;
 JSONPair: TJSONPair;
begin

  for JSONPair in LData do

Var
 LVal, JSONPair: TJSONValue;
 LData, lData2: TJSONArray;
begin

  if JSONPair is TJSONPair then
    result := TJSONPair(JSONPair).JsonString.Value;

Function GetADParamFromRendered(const sJSON, path, param_name: string): string;
Var
 LVal, JSONPair: TJSONValue;
 ad_param: TJSONObject;
 LData: TJSONArray;
 i: integer;
begin

  LVal := TJSONObject.ParseJSONValue(sJSON);
  try
    LData := LVal.GetValue<TJSONArray>(path);// 'result.ad_parameters'

    if LData is TJSONArray then
    begin
      for JSONPair in LData do
      begin
        if JSONPair is TJSONObject then
        begin

          ad_param := JSONPair as TJSONObject;// pl, vl, p или v

          for i := 0 to pred(ad_param.Count) do
          begin
            // получаем значение пары "vl"
            if ad_param.Pairs[i].JsonString.Value = 'vl' then
              result := ad_param.Pairs[i].JsonValue.Value;

            // если пара с именем "p" имеет искомое значение param_name, то и значение элемента "vl" правильное
            if (ad_param.Pairs[i].JsonString.Value = 'p') and
               (ad_param.Pairs[i].JsonValue.Value = param_name) // нашли нужный элемент category или region
            then
              exit;// нашли, в result будет нужное значение

          end;//for 
        end;// if 
      end;// for
    end;// if

  finally
    LVal.Free;
  end;

end;

Function GetADParamFromRendered(const sJSON, path, p_param_name: string): string;
Var
 LVal, JSONPair: TJSONValue;
 ad_param: TJSONObject;
 LData: TJSONArray;
 i: integer;
 s, v: string;
begin

  LVal := TJSONObject.ParseJSONValue(sJSON);
  try
    LData := LVal.GetValue<TJSONArray>(path);// 'result.ad_parameters'

    if LData is TJSONArray then
    begin
      for JSONPair in LData do
      begin
        if JSONPair is TJSONObject then
        begin
          ad_param := JSONPair as TJSONObject;

          if JSONPair.GetValue<TJSONString>('p').Value = p_param_name then
            exit(JSONPair.GetValue<TJSONString>('vl').Value);

        end;// if
      end;// for
    end;// if

  finally
    LVal.Free;
  end;

end;