Actually, for the longest time I thought it was where Clark had his home office, computer etc.
I didn't mention that last time because I remembered he had a desk in the living room - but today my memory clicked and I realised that desk was in Lethal Weapon and not in Clark's apartment.
So that's what I'd revert to. I don't think we ever saw a computer on the ground floor of his apartment, did we? Not in the living room or the bedroom.
So that upstairs area seems to be the most obvious place for it (unless I'm forgetting something). Especially if you can see from the screen that it has bookshelves in it.
LabRat