Ok, this is yet another a silly "type this person I know" case... I know there is a whole website devoted to "are you an INFJ or INFP" but it was written for the people themselves, so I didn't get much from it.
I have not known this guy long, but he did take an online test after we talked about MBTI and he scored ENFJ. I'm pretty sure that is incorrect.
This person is clearly an NF, the N is very strong (he's a successful scientist, a theorist, actually) but as an NT I can see that he is not one of us. When asked directly he said "how you feel about something is the most important thing in making a decision" (as opposed to logic). He's very sympathetic (to me) but I have not known him long so I can't say if that is a universal thing.
I'm pretty sure he's an I, he's mentioned that he prefers small groups of close friends and abhors a party where he knows few. He seems to like being alone, though he does have a lot of friends.
The J/P question... this is not the first time I've had trouble telling. Sometimes I think it is the most flawed of the 4 attitudes.
He seems open to new things, certainly not dogmatic about religion or rules, doesn't seem to have a definite schedule to his days (but I don't know him THAT well), and seems ok with uncertainty. On the other hand, he doesn't seem to have difficulty making decisions, his house is tidy, has no problems being direct communicator ("put that there, not , "that should go there"), and professionally he has been very succesful (not saying P's aren't, just that he reminds me almost of an INTJ in this respect). On a recent trip he definitely had a big print-out of information about every place we were going or might go and maps, etc.
What should I be looking at to tell? Does it really matter? Well, kind of. I have a relationship with this person and I'd like to know if we're likely to have J/P clashes, or if we're both going to become a giant pile of P-ness.