which Mechanical Master course is best and have high demand in future - product design engineering or automotive engineering or manufacturing engineering?

Hey, the mechanical master’s course that is most in demand is Master of engineering in Tool Design. After mechanical engineering, it is once again one of the most promising postgraduate courses. The course is best suited for those who can tackle problems analytically and creatively. The career roles available to candidates upon successful completion of the course require greater depth and precision. Some other courses that you  can target are:

Piping design and manufacturing 
Robotics
Mechatronics course
Nanotechnology course

You can choose between product design engineering and automotive engineering from the alternatives you've provided. Because these two are design-based, they are in high demand and will continue to be so in the future. If you have any further questions just ask me.