Does SoK require Prepaid NX?

I don't even know how to tell.

I don't think they do, if you roll over them and in the picture of the item, there is a large green NX symbol, that means it needs Prepaid NX.

If you want to see the symbol, look at Gold GAchabox keys, I know those have it. World Transfers should too

It does not. You can tell by hovering over the item and seeing if the item icon has a regular cash coin next to it or the NX symbol (prepaid).

EDIT: Ninja'd

You can buy those with any type of NX.

Only items with the green "NX" icon (when you hover them) are limited for NX Prepaid:
http://i50.tinypic.com/15henma.png

And that's Karma icon:
http://i49.tinypic.com/2elr321.png