While scarifying is an alternative, it is not necessary, any more than
stratification. It may influence germination, but in nature, it
doesn't happen that much, scarification that is. Nursery's stratify
black walnut, but seldom scarify, just as they stratify other seed.

In nature, scarification happens by a seed coat being gradually worn
away or a seed coat being cracked by freezing. Scarification is a way
to speed this up (with cutting a notch and hot water seeming to be the
preferred techniques). At least, that's what my book on propagating
woody plants says.

But each plant is different. And I don't know anything about black
walnut in particular.

Getting some instructions from someone who has propagated the
particular plant in question is recommended. Sure in nature, the
plant grows (somehow). But whether this happens quickly, or how many
seeds are needed for one seeding, or whether the seed passes through
the digestive tract of a bird or mammal in nature, or whether you can
keep a seed in the ground for months/years and recognize it as a
non-weed when it does come up, or whatever, make the garden situation
often different.