When my creature successfully attacks with an encoded cipher card attached, does the copy also have cipher? Wouldn't I be able to encode the copy of the original spell onto a new creature, having 2 creatures encoded, 1 from the original cipher and 1 from the encoded copy?
The first rule for Cipher says
Cipher appears on some instants and sorceries. It represents two abilities. The first is a spell ability that functions while the spell with cipher is on the stack. The second is a static ability that functions while the card with cipher is in the exile zone. "Cipher" means "If this spell is represented by a card, you may exile this card encoded on a creature you control" and "For as long as this card is encoded on that creature, that creature has 'Whenever this creature deals combat damage to a player, you may copy the encoded card and you may cast the copy without paying its mana cost.'"
When you first cast the spell with Cipher from your hand, it is a card, so you can encode it on a creature. When that creature deals combat damage to a player, you can cast a copy of the encoded spell. That copy is not represented by a card, so you can not encode it on a creature.
Taget player loses 1 life, discards a card, then sacrafices a permanent.
Cipher (Then you may exile this spell CARD encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a COPY of the encoded CARD without paying its mana cost.)
This wording infers that the controller is copying a CARD not a SPELL so..... YES, YOU SHOULD BE ABLE TO ENCODE IT TO AS MANY CREATURES AS YOU WANT BECAUSE YOU'RE COPYING A CARD NOT A SPELL