Interested in Language
Can since be at the end of a question, the same way as other prepositions can?
For what? What did you come here for?
From which? Which policeman will you get this from?
You might hear "What date/When have you been here since?"
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Note that in ems' sentence, 'since' requires the present perfect, because it refers to a time that began in the past and goes up until the present.
That's why your titular sentences are wrong.