How to calculate Total Working Hours (8 per day) for Whole month excluding Saturday-Sunday Weekend ?

You are really asking how to calculate the number of business days between two dates.  Fortunately, there is a function for that, and also functions to know the first day of the month and the last day if the month.

You will need to which month you are talking about but if you wanted to know about the current month it would be

This would be the formula for the current month

8*
WeekDaySub(LastDayOfMonth(Today()),FirstdayOfMonth(Today()))