In this sentence: Перед обязанности затем удовольствия can you tell me in which cases are duty (dative, genitive, prepositional?) and pleasure (genitive? plural?)? can you help me? thanks
The sentence is incorrect even excluding cases of обязанности and удовольствия issue. And the answer depends on what do you really mean.
If the sentence supposed to be
"сначала обязанности, а потом удовольствия"
then it can be helpful to insert skipped verbs here:
"сначала [идут] обязанности, а затем [идут] удовольствия"
In this case, it's easier to see that the case is nominative.
The sentence sounds strange. Better would
Сначала обязанности, затем удовольствия or
Вперёд обязанности, потом удовольствия
When I think on cases it's difficult for me to distinguish (perhaps someone will correct me here). Both would be either Nominative or Accusative.
I should also mention the Russian sayings/proverbs, that suit better here and mean the same thing you'd like to express:
Сделал дело - гуляй смело and
Делу время, потехе час