Well...you could suggest therapy pointing out the person seems depressed to you...or other symptoms, if this doesn't fit.
If they are truly N, they may rage - or later, years later, may actually think about this. Usually it takes a pretty big narcissitic injury for a person with NPD to seek help.
As for us raised by Ns and just displaying lots of N characters (hey - it's
about all we've ever been praised for by them) - we seek therapy more readily, I believe. I think this is because we are already convinced there is something terribly wrong with us.
I have been seeing my current therapist at least twice a month now for over 10 months. I still ask her: Karen, what if there is something wrong with me, and you just don't know what it is cause I don't act like that here in your office? You don't see me at my worst...
She keeps insisting my only problem is that I need reparenting. We all make mistakes - she said. The difference is some of us want to change and do have the ability to change. Ns don't want to..
I guess maybe that's a good test then: ask them what
they'd like to change about themself. If you get a big
HMMMMMMMMpppff you'll know

Could you give us some more details of what makes you suspicious? You seem, not
too worried...just by your positive sounding post. Do you think they can empathize? Are they aggressive, and if so in what ways? Is this N person close to you? A friend or coworker? Or are they an important relative? When I was new here I kept thinking someone I knew would recognize me, so I didn't post a lot of details. Despite calling my Ns what I think they are (N), over and over, for more than a year now.. They still haven't shown up yet (you'd think they'd google it and find us here)- so I think I'm safe (you are too!)
hugs,
bean