[SQL Data] how to upload a file in SQL server?

I don't think you'll be able to use the 'SQL Data' even to upload this because this template creates a straight SQL statement under the covers (you can view it by clicking "Edit Code" for this event).  As I understand it in ADO.NET, binary data must be inserted via parameters. 

You could write the parameterized ADO.NET code within a Server Event.  The ADO.NET would expect a byte array (byte[]), which is the actual binary data.  This can be retrieved via the below call (where "EmbeddedFile" is the binary process data field).

 byte[] oBuf = (System.Byte[]) K2.ProcessInstance.DataFields["EmbeddedFile"].Value;

At this point it you can write normal ADO.NET code within the server event to insert the binary data.  There are a number of examples on the internet that show how to insert Binary data into SQL via ADO.NET via the use of a paramertized query.

You will not be able to do it using SQL Data event. Use Server Event with custom code instead, where just put bytes from your binary field manually.