Este código fará o que você deseja (obviamente, altere o nome da tabela, o nome do servidor etc.):
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
namespace ConsoleApp
{
class Program
{
static void Main(string[] args)
{
string query = "SELECT * FROM t where 1=0";
string connectionString = "initial catalog=test;data source=localhost;Trusted_Connection=Yes";
DataTable tblSchema;
using (SqlConnection cnn = new SqlConnection(connectionString))
{
using (SqlCommand cmd = cnn.CreateCommand())
{
cmd.CommandText = query;
cmd.CommandType = CommandType.Text;
cnn.Open();
using (SqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.KeyInfo))
{
tblSchema = rdr.GetSchemaTable();
}
cnn.Close();
}
}
int numColumns = tblSchema.Columns.Count;
foreach (DataRow dr in tblSchema.Rows)
{
Console.WriteLine("{0}: {1}", dr["ColumnName"], dr["DataType"]);
}
Console.ReadLine();
}
}
}