How to get a string from list of objects and not from a list of strings and display randomly?

I am trying to make a utility for kindergarten kids that will randomly select them for stuff toys. I have an entity/POCO class and a DAL class. Then at WinForm, I am doing the random selection.

I am getting the object from the following code but I want the RollNumber field and pass it to random class.

Participants class

public class Participants
    {
        public string RollNumber { get; set; }

        public string Name { get; set; }
    }

DAL class

public List<Participants> GetAllParticipants()
        {
            List<Participants> participants = new List<Participants>();
            string Query = String.Format("SELECT rollnumber, name FROM students);
            newConnection.OpenConnection();
            SqlCommand command = new SqlCommand(Query, 
newConnection.SQLConnectionInstance);
            SqlDataReader dataReader = command.ExecuteReader();
            Participants participantList = null;
            while (dataReader.Read())
            {
                participantList = new Participants();

                if (System.DBNull.Value != dataReader["rollnumber"])
                {
                    participantList.RollNumber = 
(dataReader["rollnumber"].ToString());
            }
            if (System.DBNull.Value != dataReader["name"])
            {
                participantList.Name = (dataReader["name"].ToString());
            }
            participants.Add(participantList);
        }
        return participants;

    }

This is how I am trying to get the rollnumber field

    public string RandomString() {
        ParticipantRepository participantRepository = new ParticipantRepository();
        var listx = participantRepository.GetAllParticipants();

        var listP = new List<Participants>();
        var mySKUs = listP.Select(l => l.rollnumber).ToString();

        var zoo = mySKUs.OrderBy(x => random.Next());
        var xoo = zoo.ToString();
        return xoo;
    }

And trying to show it in a label at timer_tick event but this is what I am getting instead System.Linq.OrderedEnumerable'2[System.Char, System.Int32]