@Malin one of the most useful questions for me is, am “I comfortable being perceived as [binary gender]?” Because that’s mostly what it comes down to, in my opinion. If I lived alone in the woods and never spoke to other humans I would never know I was non binary because no one would be there to perceive and judge me.
There’s also a feeling called Gender Euphoria which is the feeling of joy and validation a person gets when they’re correctly gendered (opposite of dysphoria). It’s a big tell 💜