Plug-in on Korean Air 747-400?
 

I visited seatguru.com, and it looks like only first and business can plug in. Are there no other power plugs anywhere on the plane? I'll be flying economy. Also, what kind of plug will I need?

Although I do not have first-hand experience, I'd trust SeatGuru with regard to the location of the plugs and the type of power solution on the plane. What their site says about the 744 is:
This means that if there is a plug it will be a standard outlet, not emPower or some other "special" outlet.

Not sure what route you're flying on, but you can probably find out the Korean forum here which routes are likely to have the planes with plugs in the back, if the planes are on specific routes.