Student or Learner
Is it grammatically correct to ask someone to work on something by telling this
"you are going to work on this"
The GRAMMAR in "You are going to work on this." is correct. (Note my changes.)
That is not at all the same thing as ASKING someone to work on something, which is what you asked.
It's also not how polite people talk to each other in the workplaces I've been to, even if the person telling me this had complete authority over how I spent my time.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.