I may be a little dog, but I'm not silly!
What will you be doing next tests you on future structures.
English has a wide and subtle range of Future verb structures: here's your chance to grapple with them once again and to distinguish their formation and purpose. 'What will you be doing next?' Wait and see, from Question to Question!
The second element (complete with contraction) is a very natural way to express a potential future event that is much less certain, and probably not 'fixed' ~ certainly in the current speaker's mind ~ in the same way as the front part of the situation. We use this form (usually contracted) when predicting, from past experience ~ as here ~ how matters may develop. ('If I know Uncle Charles, he'll have had a drink or two before he gets here.')