You're not going to get a demo of InFamous Second Son - so you'd best make do with this afternoon's (UK) upcoming iFSS live broadcast that you can see below.
What? No demo? Nope, inFAMOUS: Second Son has confirmed that, "I don't think we're going to have a demo," he said before continuing:
"It's hard to have a demo with an open world game to be honest with you. You what, pick two missions out of the whole thing then you give them a little slice of the world, you gotta make all these walls? I don't think [having a demo] does justice to an open-world game," he told Videogamer