Which of the following preposition is correct to talk about some events?

Good Evening!
Which is correct:
Why you didnt come to the party?
Why you didnt come in the party?
Why you didnt come on the party
and
Why you didnt come in the graduation day?

Correct sentence:

Why didn’t you come to the party?
Or
I want to know why you did not come to the party.

Hi Luby
I think the correct one is to
but don’t ask me why
I can’t explain
my regards

Good Evening people!
Thanks for your response,but I want to is the last sentence correct,because it is refering to a particular day?

I want to know why you didn’t come to the graduation day? or.
Why didn’t you come to the graduation day?

Good Evening!
Thanks for clarifying and sorry for late reply because I was just checking my mails today and received a this today only.
I think from now on I will send a PM if I have any questions,because I am sad that most of my questions havent been answered. :frowning: