Which python modules i must learn???

Answer 1

extremely debatable. it's all up to you what path you choose to specialize in
for a starter it's ok to know about collections, itertools, functools, datetime modules.
for data science: numpy, matplotlib, pandas, scipy modules are a great plus.
for AI: sklearn and tensorflow modules are a great plus.
for desktop apps: tkinter, pyqt5 (the last one is better) modules
for gaming: pygame, arcade modules
for mobile apps: kivy module
the built-in modules are very important though, especially collections, itertools and functools

Answer 2

Some important libs for beginners:
random, numpy, pygame, re, math, time, itertools
Extras for higher level programming:
tensorflow, pandas, tkinter, matplotlib, etc