If Joe would lose 2 pounds a week his intake is 4200 kcal a day and his energy expenditure does not change how many kilo calories should he consume each day to achieve his goal?

To lose two pounds a week, as long as 4200 kcals are what Joe actually needs to simply maintain his current weight; Joe would need to lower his kcal intake to 3,200 kcals (7,000 kcals less per week = ~ 2 pounds of fat a week.)

However, it is likely that it would be better for Joe to exercise for 30 minutes each day burning roughly 200 kcals a day, and reduce his intake by only 800 kcals per day to 3,400 kcals. Anyway... there are a number of different approaches to reach the goal, but diet and exercise should be used.

Also, 4,200 kcals seems higher than most men would need to simply maintain weight unless Joe is already burning the extra kcals due to exercise.

Good luck Joe.