First of all, do you have a rulebook?
If not, I'll summarize the event for you:
Shock Value is basically about electricity, magnetism, and electrical devices. You get some hands-on stations and then a couple of more traditional stations involving diagrams, graphs, or questions. You should understand basic DC current theory, basic electrical concepts, and be able to build/analyze a circuit. You should also know about basic magnetism concepts and applications.
So look at the wiki (here: http://www.scioly.org/wiki/Shock_Value
), google some stuff, build some circuits (without electrocuting yourself), find out about magnets and you should be relatively prepared.