What is the SQL Server equivalent for Oracle character set AL32UTF8?
NVARCHAR is always UTF-16.
You can try Latin1_General_100_CI_AS_SC_UTF8 with a VARCHAR column, but that doesn't look like an encoding problem. It really shouldn't matter what the source encoding / collation was as long as you correctly indicate the encoding used to transfer the data.
Either way, those 3 bytes / characters could be a bug in the import tool/process or the export tool/process. How are you transferring the data? If the image you are showing from Notepad++ is from the file being used to migrate the data and the field is supposed to be empty, either the export messed up, or perhaps the field in Oracle is not truly empty.