"Where are you lying?"
Translation:Ti Hol fekszetek?
Hol fekszel should be accepted because it was not specified that You is plural (by saying you all).
In singular it would be: "Hol fekszel?"
"fekszél" isn't a valid form of the verb "fekszik".
"fekszed" isn't in use, you can't really build a correct sentence with it. Consider the verb "fut" = "run". You can ask "Hol futod le az 5 kilométert?" = "Where will you run the 5 kilometre (distance)?", so with "futod" you refer to this specific 5 km. "Hol fekszed?" in itself doesn't make much sense, because you can't lie something. To be honest I couldn't create a naturally sounding sentence with "fekszed" which couldn't be improved. But there might be some twisted sentences. I'm not sure it's worth learning them though.
"Hol fekszed le a kötelező 5 órádat?" --- "Where will you do your compulsory 5 hour lying?"
I'm still trying to get my head around the use of van, I thought you had to use it when saying where something/someone is. Does this not count as that?
Yes and no. You do use van when saying where something is, but van is not used in every situation that involves discussing a location. Van means, as far as I understand it, 'there is.' But you can still ask questions about location without using it. Ex. "hol fekszel," "hol laksz," "hol vásárolsz" etc.