What kind of "then" is meant here?
Is it strictly time-related, as in "What are you going at that point in time?" ?
Or is it the kind "Well, if you're not reading a book and you're not eating breakfast, what are you doing then?", where "then" is something like "instead of the previous options" ?
This is a funny one. I always want to answer "What will you do then?", but it's not accepted, and the 'correct' answer sounds really odd. I could imagine it making sense in some contexts, eg. "If you're not a doctor, what do you then?", or "If you're out of options, what do you do then?". But by itself, it's really odd. Anyone else think this?
Ad 'Mit csinálsz akkor?' - I admit this is really a valid example. But, in this case 'akkor' means something different, it does not refer to a specific time, it somehow stresses the distinction. 'Megeszem az áfonyás muffint.' 'Akkor enyém a csokis.' ('I am taking the blueberry muffin.' 'Then I am taking the one with chocolate.')
Ad "fogsz" - what are referring to here?