do you know or can someone guess how fat will you be, if you are eating 1 cheeseburger daily/year?

It depends on the following:

1-The nutritional values of that cheeseburger

2-Your daily energy/calorie need

3-Your diet apart from that burger, is it the only the only thing you eat in one day, what you eat usually and so on.

4-Your time preferences and daily activities and initial weight.

you should provide those information to a doctor or a nutrition professional and ask for assistance.

That would depend on what other foods and fluids you are consuming in a day. Sugars in these other things would greatly increase weight gain.:)

Prob not very if thats all you eat.