With быть + inf. it would be better to say "What will we be discussing tomorrow?"
It seems that DL always wants обсуждать to be 'discuss'. I more naturally say "talk about". I've suggested that this be changed. Can anyone tell me more about this?
What shall we discuss tomorrow - slightly better grammar than will ( not sure why but that was what I was taught). Shall is not accepted by dl
This may be 'better' grammar according to a textbook, but it's much more natural to say 'will.' I never use the word, "shall" unless I'm teaching from a British textbook like the ones produced by Cambridge.