Cherry is basically right. "You should have known this" This is information you should have known at that time (but for some reason, you did not). (Mom will be upset that you joined the army. You should have known this.) (Why did you give him a peanut butter sandwich yesterday? Dad is allergic to peanuts. You should have known this.) This is related to: You should have known. (Dad should have told you, you were adopted.) You should know better. (You're already 30 years old. Don't pick your nose.) You should have known better. (Last Friday, you shouldn't have been driving after drinking.)

Hello Antman, "You should have known this" No ,it can't really mean " I am not sure if you know it or not". "Should have " doesn't refer to any uncertainty or possibility. It expresses rather that you did not know it ,but the person wishes it had happened. You use it when you are saying what would be the right thing to do or the right state of something to be in. " You should know this". If " should" is used without "have" here the meaning is different. You could be giving someone an order to do something . It could mean that it is probably the case that you know it ( my guess is that you know this ) . It is used when you are giving someone an advice." You should know this" (it i recommendable that you know this).

Hello Antman I think you understand the meaning here and it depends of the context and also the intonation...