I put "nebojíš se ničeho" too and it said it should be "se nebojíš ničeho" but I didn't think se can come first
That is a mistake, I will fix it.
"Ničeho se nebojíš?" je taky spravné, ne?
It is a question. Why the sentence is not: "Are you not afraid of anything?"
This is the affirmative question word order http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv333.shtml