I attach Shady Spectacles to a non-token unit and make it a copy of Ekko Recurrent. If that unit dies, can I ready my runes if I recicle the unit? The deathknell trigger should be on the stack, but can it even recicle a card like Soaring Scout if that card was an Ekko Recurrent when it died?

Yes — you can recycle the Soaring Scout and ready your runes.

While Shady Spectacles is attached, the unit's rules text is replaced by Ekko's (copyable traits), so it dies with Ekko's [Deathknell] — Recycle me to ready your runes and that trigger goes on the Chain normally. When you pay the cost, "Recycle me" just means recycle the card that died — recycling doesn't care about the card's name or whether it's still a copy in the trash (Rule 416). Since Soaring Scout is a real card, it's sitting in your trash as a valid recycle target.

This is exactly the flip side of the Reflection token case (FAQ #9947): a token copy of Ekko fails only because tokens cease to exist the moment they hit the trash and there's nothing left to recycle. A real card doesn't vanish, so the cost can be paid and your runes ready. Shady Spectacles becoming unattached after the unit dies doesn't matter — the trigger and its cost reference the card itself, not the gear.