Based on the data you posted, I’d say your file was the binary format rather than the ASCII format – you might want to see if you can configure it to output ASCII instead. If it’s a binary file, then likely no general-purpose text editor (be it Notepad++, MSWin notepad, vi, emacs, …) will be able to natively recognize it. It’s not an “encoding” issue, in the same way that UTF-8 vs ISO 8859 vs Win-1252 vs …
I think this question has nothing to do with Notepad++ (in that I think any other text editor – be it windows notepad.exe, vi, emacs, … – would give similar results when trying to open a binary file).
I just spent 5 minutes via search engines and https://www.openfoam.com, and couldn’t quickly find a description of the output format(s) available. Sorry, that’s all the time I have to devote to it.
My searches also revealed a forum at https://www.cfd-online.com/Forums/ . You may be able to post your question there: they might be able to help you either natively output to an ASCII text file, or to point you to a converter or post-processing manipulator to give you access to the coordinates.