Because your indentation doesn't match:
def harry():
x=20
def rohan():
global x
...
print("before calling rohan",x)
...
You have extra whitespace before the "print" instruction.
As a result, it doesn't run.
Remove those from the three lines and it prints "88"
Don't mix tabs and spaces: set your editor to always replace tabs as it'll save you a LOT of grief later. Python indentation is very important, and a TAB is not the same as a SPACE - if you don't "just use spaces" then what looks identical turns out not to be as far as Python is concerned.