Obtain the Query/CommandText that caused a SQLException

You can NOT throw a sql exception. I think he meant to throw a new Exception that contains the command.CommandText.

The SqlException does not hold a reference to the SqlCommand that caused the exception. In your logger there is no way to do this. What you could do is catch the SqlException in the method that executes the SqlCommand and wrap it in a more descriptive exception. Example:

using (var command = new SqlCommand(connection, "dbo.MyProc"))
{
    try
    {
        command.Execute();
    }
    catch (DbException ex)
    {
        throw new InvalidOperationException(ex.Message + " - " + command.Text, ex);
    }
}

This way you can log this more expressive exception.

As a simple hack you can also add the sql as part of the Data of the exception. This will preserve the original exception but also give the additional sql message.

using (var command = new SqlCommand(connection, "dbo.MyProc"))
{
   try
   {
      command.Execute();
   }
   catch (SqlException ex)
   {
      ex.Data.Add("Sql",command.Text);
      throw ex
   }
}