Wrong? Je sais pas
Right: Je ne sais pas
Explanation: In French, negation normally requires two words: ne before the verb and something like pas or rien after it. So "I don't know" is je ne sais pas and "I didn't do anything" is je n'ai rien fait. In informal spoken French, however, ne is nearly always dropped, so it's perfectly normal to hear je sais pas and j'ai rien fait.
Related lessons:French negation | Informal French