#illegal targets

That works correctly. 

You need to change the target first and then grant protection to Spellskite. This will cause the spell to not affect Spellskite (and to have no effect if it has no other targets).

Giving Spellskite protection before you try to change the target won’t work because the target won’t be able to change to Spellskite as it would be an illegal target.

Spells only leave the stack when they go to resolve or when a spell or ability moves them from the stack, such as a counterspell effect.

A spell that was cast with legal targets but whose targets all become illegal stays on the stack until it goes to resolve, at which point it will fail to resolve and be removed from the stack.

A whole lot of nothing much.

Norin’s triggered ability has exiled him until the end step by the time we get to trying to resolve Clear Shot. 

Clear Shot will still resolve since it still has one legal target, which is your opponent’s creature. However, it won’t be able to give Norin +1/+1 since he’s no longer on the battlefield. Clear Shot also can’t cause an illegal target to deal damage, so no damage will be dealt to your opponent’s creature.

(If the situation were reversed, and you cast Clear Shot targeting your own creature and an opponent’s Norin the Wary, then your creature would end up just getting +1/+1 from the spell when it resolved.)

Neither.

The blinked creature returns to the battlefield as a new object. This means that it’s not the same creature that the spell was targeting and the spell won’t be able to affect it if/when it resolves.

When the spell goes to resolve, the creature it was targeting is no longer on the battlefield and thus not a legal target. If that was the spell’s only target (or all of the spell’s other targets are also illegal now), then the spell will be countered instead of resolving. If the spell had other targets and at least one of those targets is still legal, then the spell will resolve and do as much as it can to the remaining legal targets.

It has nothing to do with punctuation or line breaks.

A spell with a single target will be countered and thus have none of its effects happen if its target is no longer legal when the spell tries to resolve.

For example, you cast Slip Through Space targeting your creature, but that creature dies to a Fiery Temper before Slip Through Space can resolve. When Slip Through Space goes to resolve, it sees that none of its targets are legal so it’s countered instead of resolving. You don’t get to draw a card.

A spell with multiple targets will be countered this way only if all of its targets are no longer legal when it resolves. If any of the targets are still legal, the spell will resolve and do as much as it can, though it won’t be able to affect the illegal targets.

Yes.

When Ruinous Path is cast for its Awaken cost, it targets both the creature or planeswalker it would destroy and the land it would awaken. It will only be countered on resolution if both of those targets are illegal at that time.