Can I look at the bottom card of my deck before putting it under Nemesis Prime?
[Source: WotC]
No. Neither you nor your opponent will know what card it is.
What happens to the cards under Nemesis Prime when he’s KO’d?
[Source: WotC]
They’re put into the scrap pile, along with any Upgrades he had.
That is correct.
If I'm attacking with Nemesis Prime and in the course of my attack burn through my deck, his ability triggers and I shuffle. Once done shuffling, the bottom card goes under him. Does he instantly get the +3 attack, or does it get added to his next attack?
[Source: WotC]
He gets the +3 attack instantly.
Does Nemesis Prime keep his attack power from recycling scrap when he transforms to truck mode?
[Source: WotC]
The ability that grants the attack bonus is not on his truck mode, so it does not increase his attack, although the face-down cards remain under him.
If I have Shockwave in play and my opponent has 2 characters with 1 damage left each (say
Optimus Prime - Battlefield Legend with 13 damage and Nemesis Prime with 15 damage) and I play
System Reboot forcing them to discard 2 cards, can they choose to put both damage on Nemesis Prime or must they put 1 damage on each?
[Source: WotC]
Each card discarded creates a new instance of 1 damage, so they will be forced to put one damage on each.