"Where are you lying?"
Translation:Ti Hol fekszetek?
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?"
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.