What does `/n "%1" /o "%u"` mean?

A preliminary answer without being entirely sure of the full command you ran:

The command-line arguments supplied to CMD when opening a program can be elusive, at best. They're not actually arguments of the ftype command you ran, but a mixture of arguments from different high-level commands that Windows uses to run commands and programs from places like the Windows Registry. You're seeing them because the ftype command you ran returns the full path name, at the end of which the arguments being called to open the program happen to be included.

Some of these arguments are documented, as part of the cmd command and the start command (see the File Associations section for the RVD link).

Others are also documented, but much harder to come by. The linked answer is the only list of command-line arguments for opening a program that I've been able to locate among all the StackExchange sites, and the information in it comes from a now-deleted comment on an obscure source from the Microsoft Developer Network site (!).

Yet others aren't native Windows arguments, but are created and defined by the program that runs them. For example, according to this on Microsoft Word, Word has its own command-line arguments, one of which appears first in your list above. According to that link, the /n argument is used by Word to initiate a new instance:

/n

Starts a new instance of Word with no document open. Documents opened in each instance of Word will not appear as choices in the Window menu of other instances.

You correctly guessed that the %1 parameter refers to the filename being passed to the program, but everything that's left is likely a global command-line argument that Windows (idiotically) decided should remain undocumented.

Finding out what those are is probably something that can only be done by you, and would involving using echo to determine the contents of those arguments.

References

CMD.exe - Windows CMD - SS64.com

Rob van der Woude - Batch files - The START command

Which special variables are available when writing a shell command for a context menu

How to use startup command-line switches to start Word 2010, Word 2007, Word 2003, Word 2002, and Word 2000