Ok so problem is that my Skyrim box doesn't have product key inside it.. I asked my friends and they told it should be inside it in a sticker, but I dont have any. I also checked the manual and map if the key is there but nope. What should I do?

take it back to where you bought it and ask for a replacement?

Take the product back man. I read this topic title going "No..No...no no no." But nope. Same thing happened to my friend . svcks man. Blame production on this.

Was it a sealed box ?

Yeah the box was sealed.. I hope the store accepts it back now that it is opened.