Edit 1: Seems like apply is always bad, seems like a more accepted solution is to use list comprehensions.
df['new_column'] = [str(x).split('.')[-1] for x in df.iloc[:,0]]
DON'T DO WHAT'S BELOW
I think this is a good instance for using apply. You might not need the str call.
What this is doing is taking the values in your column (aka a Series) and applying a function to them. The function takes each item, makes it a string, splits on the period, and grabs the last value. We then store the results of all this into a new column.
df['new_column'] = df['column'].iloc[:,0].apply(lambda x: str(x).split('.')[-1])
should result in something like what you want