The possessive form of "day" is "day's." For example, you might say "today's weather" to indicate the weather of this day.
No, singular possesive. There's only one St. Valentine and it's his day.
his
goose's
pilot's
enemy's
Actress'
dictionaries'
His and my are possesive pronouns.
everyone's
Classes can be the answer
all together-possesive altogether-non possesive example: All together kids
all together-possesive altogether-non possesive example: All together kids