Saying it did not happen

The negative uses the fused forms you already know from бити - нисам, ниси, није, нисмо, нисте, нису - followed by the same participle. Нисам радио means “I did not work”; there is no separate не here, exactly as in the present tense.

To ask a question, put да ли in front and leave the rest alone: Да ли си радио? Word order doesn't change - same rule as in the present tense.