How to load data from database to ajax and get values back on front end by asp.net?

string constr = "Server = 192.168.248.212; Database = testdb; Trusted_Connection = True;";
int i;

i = 0;
SqlConnection con = new SqlConnection(constr);
SqlCommand cmd = new System.Data.SqlClient.SqlCommand();
cmd.CommandText = "select * from LoE";
cmd.Connection = con;
con.Open();
SqlDataReader reader = cmd.ExecuteReader();

con.Close();