Question 1: One damage is prevented to the 6/6, and the 6/6 keeps 1 damage prevention until expended or end of turn. Reason: The scorpion doesn't do any damage, so it's deathtouch ability doesn't work.
118.8. If a source would deal 0 damage, it does not deal damage at
all. That means abilities that trigger on damage being dealt won’t trigger. It also means that replacement effects that would increase the damage dealt by that source, or would have that source deal that damage to a different object or player, have no event to replace, so they have no effect.
Although deathtouch is not a triggered ability, it's still circumvented because:
702.2c A creature that’s been dealt damage by a source with deathtouch
since the last time state-based
actions were checked is destroyed as a
state-based action. See rule 704.
Question 2: More comprehensive, but your opponent gets to choose in this situation:
615.7. Some prevention effects generated by the resolution of a spell
or ability refer to a specific amount
of damage—for example, “Prevent the
next 3 damage that would be dealt to
target creature or player this turn.”
These work like shields. Each 1 damage
that would be dealt to the “shielded”
creature or player is prevented.
Preventing 1 damage reduces the
remaining shield by 1.
If damage would be dealt to the
shielded creature or player by two or
more applicable sources at the same
time, the player or the controller of
the creature chooses which damage the
shield prevents.
Once the shield has been reduced to 0, any remaining damage is dealt normally. Such effects count only the amount of damage; the number of events or sources dealing it doesn’t matter.
