Shouldn't "What are you doing on Tuesday" be accepted? Or am I missing something?
A what are you doing - present continous- folyamatos jelen.
What are you doing at the moment ? - Mit csinálsz most?
What do you do- present simple - egyszerű jelen
What do you do (usually) on Tuesday? - Mit csinálsz (általában) kedden?
"What are you doing on Tuesday" should certainly be accepted. Report, report.
What will you do on tuesday - seems to me more logic, but it was marked wrong.
What will you do on tuesday? = Mit FOGSZ (will) csinálni kedden?
So it is "kedd_en" because it is meant to be usually on that day and not only one tuesday? Otherwise it was simply "mit csinálsz ez kedd?"
kedden = on (this) Tuesday
keddenKÉNT = usually on that day and not only one tuesday
"What are you making on Tuesday?" got rejected. Why?
The meaning of make is rather create something, but English asks in general as do can refer to anything - including making/creating something. I would translate your sentence with make like this: "Mit készítesz kedden?"