How many pounds will you loose if you dont eat for 2 days?

You will lose some. But that isn't particularly important, as unless you change your lifestyle you will begin putting it right back on the moment you return to your previous eating habits. 20 days is a bit on the long side too, if it's on water-only you're well in the realm of where medical issues can arise. Not to mention that you're unlikely to be able to to fulfil any job obligations particularly well during this time.