Very individualized as per need. Non-binary is an umbrella term for a whole bunch of different situations so what feels right is going to be very different for someone who feels like say a mix of masculine and feminine versus someone who has dysphoric reactions to any and all gender markers. It’s going to be different for someone whose identity is more static than say someone who fluidly bounces between extremes.

If you know someone who is non-binary that’s essentially just the tip of the iceberg of a whole discussion about how they personally interact with their body or the culture of gender. I’ve heard of mixes of Mom/Dad for bigender people, just Mom or Dad for trans masc/femme folk, Completely new words that do not have cultural baggage, or just “my parent”. It’s not a one size fits all situation.