Translation:Dzisiaj w nocy
"tonight" can mean evening or night, e.g. "see you tonight" would imply "this evening", whereas "I'll sleep well tonight" would imply during the night. Both are correct in English, but can be confusing! You could also say "see you this evening" if you want to; it means the same as "see you tonight".
The word in the exercise is shown on its own - without context - therefore knowing if they mean "evening" or "night" is impossible. If the exercise said, "see you tonight", or "I sleep at night", then there would be enough context, but it doesn't. Without context, both answers should be accepted.