How to find which columns contain any NaN value in Pandas dataframe

Question

Given a pandas dataframe containing possible NaN values scattered here and there:

Question: How do I determine which columns contain NaN values? In

Answer 1

Both of these should work:

df.isnull().sum()
df.isna().sum()

DataFrame methods isna() or isnull() are completely identical.

Note: Empty strings '' is considered as False (not considered NA)