As Hanno Binder suggested in his comment:
Atmel Studio still does not provide any means to display debug messages sent by the program simulated. Your only option is to place breakpoints at apropriate locations and then inspect the state of the device in the simulator. For example the locations in RAM where your result is stored, or the registers in which it may reside; maybe have a 'watch' set on a variable or expression.
I think this is the best answer, watch vairables and memory while in debug mode.
Note: turn off optimization when you want to debug for infomation, or some variables will be optimized away.