Am completely bemused as to why teens lack of knowledge about any of those things, would worry you 
Not knowing which set they are in - Clearly, it's not important to them. If they are progressing or not is important, but if they are in a higher or lower set than someone else, isn't (that's if they do set, not all schools do, and many set in some subjects only)
Not knowing which sets are higher than others (have some sort of bizarre letter rating system) - see first answer
Thinking it takes six hours to cook a chicken - why would it be important to know this ?
Firstly, it could take that long in a slow cooker, secondly it's not a general knowledge I'd expect many people to have, unless they were cooking a chicken on a weekly basis, and thirdly, surely if they were about to cook a chicken, they'd read the instructions at that point in time?
Not knowing what I.C.T stands for even though they take classes in it Am a bit surprised they don't know that, but I've just checked with my 15 yr old, and she tells me it's not called that anymore, it's IT these days.
One of them (15) saying they want to be a Police Person when they grow up Don't see what's wrong with this one either - I suppose Police Officer would be more correct, but they were clearly just trying to avoid saying 'man' or 'woman' as they are aware it could be either.
One of them (15) saying the Harry Potter books are too complicated Well, if you don't like reading, then I guess they are quite involved dunno, never appealed to me, and I do like reading. It's comparable with a sports move or playing a piece of music - not complicated if you are a County player or a Grade 8 player, but pretty tricky if you always hated lessons and gave up your violin when you were 10.
Being unable to locate eastern Asia on a map Well, it's not a country as such is it. What reason would they have for needing to? I often hear of places on the news that I don't know where they are, and I'm old enough to have done Geography a LONG time ago --before half the world changed to become different countries*
Really not sure what you are trying to say in this thread.