You provided a screenshot, but I am doubtful any of of the regulars here have enough experience with Korean to understand what you seem to think is wrong with the above. Maybe a better description will help.
But I will try some wild guesses, to see if I can be of some help to you.
Assuming you are trying to show that a few of the glyphs on the left are showing up as a ? in Notepad++:
if you did a bad encoding conversion, where the destination encoding didn’t have a codepoint for your source character. For example, if you took text ☺ U+2640 SMILE, and tried to use Encoding > Convert to ANSI, it would change from395a185d-610f-4a8b-ae32-42fa7d7fbda1-image.png
to
? `U+2640` SMILE
3b7eb59d-6e7c-47de-ad46-4d3d1c193647-image.png
because there is no glyph in ANSI for the ☺ smile character. Similarly, if you tried to paste that text into a file that was already an ANSI file, it would do the same conversion to ? `U+2640` SMILE so maybe you are trying to convert text into or paste text into an encoding that doesn’t have a codepoint for the Korean character that becomes the ? Or maybe your chosen font for Notepad++ doesn’t include glyphs for those characters (but I think it would be an empty square box, not a question mark). Using Settings > Style Configurator > Global Styles > Default Style to pick a different font which you know has that glyph might solve the problem. (Or maybe changing the Settings > Preferences > MISC > ☐ Use DirectWrite and restarting Notepad++.) Or maybe it is showing something like one�two – which would indicates that it was trying to decode some bytes from your file as a unicode character, but it wasn’t a valid unicode character, so it displays the � symbol to indicate a data input problem. This might indicate that your original file has some bad bytes (either because something was corrupted, or because the application that created your text file made a mistake).