"Hi there, in order to write our customer sales report, I need to know the possibility of ' will ' ... in Jan. Does it mean 100% possibility? or 50% possibility? I want to know the possibility of ' will '."
It's not that simple. "Will" has a number of different usages. In your case the most important are:
a) Spontaneous intention at the time of writing.
b) Future fact, e.g. "Tom will be 40m next Saturday".
In this context it would appear that b) is the more likely. So it could be 100% probability. But to be absolutely certain I'd need to have more context. i.e. not just the sentence on its own.
Regards, Einde O'Callaghan