Where's Johnny?
Here.
Why is the sky?
Because otherwise there wouldn't be a sky, and then what would we pan up to all the time?
What color is G-Sharp?
It doesn't matter. It's not a G1 homage, so it's neon.
What is the front of a classroom? Is it the area where the teacher stands and writes on the board, or the area where the door to the outside of the classroom is?
The former. If there are multiple boards that the teacher uses, there is generally a desk or podium of some sort that marks the front, and also the desks typically face the front of the classroom (although not in some classes).
Who's there?
Applesauce.
Who is heh, man?
The Internet counterpart to He-Man.
Nepal / 3?
Julius Caesar.
Alternatively, it could be Augustus, with a remainder of allegory.
What is 5 / 0?
#DIV/0!