Via neuroscience means - possibly. In person - not a chance.

Forget all these things about appearances. How such person would appear graceful, loving, serene to you. All of that is bullshit and a projection of your ego. There are people who seem to radiate love and acceptance, but those people are undergoing the transformation, they are not enlightened yet. Forget fairy tales about him being able to “transmit” his state to you, even temporarily. No one transmits anything to anyone. If it happens, it means you allowed it, and it can only happen when you’re ready.

He will not be identified unless he identifies himself and then, you’re probably not going to believe him, so ordinary he will appear to you. The best advice I could give is try to dive deep into his psyche. Ask him questions about himself, his motives, his views, his morals, his perception of life. Really try to understand him, to relate to him. This assumes he is cooperative and tells you what it really is like to be him, rather than what you want to hear.

Now, if the outcome of this exploration makes you more confused about him than before, there’s a good chance he’s enlightened. You will not be able to understand him. You will not be able to relate to him, on a personal level. The deeper into him you go, the more crazy he might appear to you. He may even appear evil and totally lacking moral virtues. You may feel uncomfortable around him, fearful, even. It will be very hard to build what people call “a genuine human connection”. You may experience a lot of negative emotion towards him, even though you will not see any signs of him experiencing any negative emotion towards you. Your head might spin. You might get a headache. You might feel exhausted.

If all of that happens when you’re trying to really get to know what you would call “his inner world”, there’s a good chance he is enlightened.

His cooperation is key here. He will see all of that happening to you and he will know his answers make you dizzy, confused and uncomfortable. For him it will be, in a certain way, like having an adult conversation with a child. Not all adults want to. You kinda have to ask him. And just like in this example, if you start arguing with him about him, he will have absolutely no reason to argue back, so the adult conversation will probably cease and he will tell you exactly what you want to hear just to get rid of you.