Solution
import pandas as pd
def duplicate_emails(person: pd.DataFrame) -> pd.DataFrame:
results = pd.DataFrame()
results = person.loc[person.duplicated(subset=["email"]), ["email"]]
return results.drop_duplicates()
if __name__ == "__main__":
data = {"id":[1,2,3],"email":["a@b.com","c@d.com","a@b.com"]}
df = pd.DataFrame(data)
print(duplicate_emails(df))