Querying Utf 8 with C# by Using Prepared Statement

Sorry if this question is duplicate and also very simple question. However I can't solve my query problem. I'm new to C# queries. I need to do query like " select * from table where att=N'ğasd' ". I have to use N, otherwise it does not match.

I want to use prepared statement, but when I do something like:

commandString = "select * from table where att=N@param;";
command.Parameters.AddWithValue("@param", "ğasd");

It gives " Invalid column name 'N@param' ".

My attribute is nvarchar(50). There is also another interesting thing. Another attribute like att2 is also nvarchar(50) and my database's collation is "SQL_Latin1_General_CP1_CI_AS", but att2='ğasd' works fine. I solved this problem with adding "N". This time like I said, I stuck on prepared statement problem.

Am I doing something wrong? please help.