I'm already so used to calling it svenska that I answered "Do you understand svenska" which it counted wrong. Forgot for a moment that the English people call it swedish there
I'm having trouble understanding the syntax of this sentence. Is this what ive heard called a helping verb? Might an answer to the posed question be "ja, det förstår jag"?
There's no helping verb here in Swedish, it's just the normal question word order. In all direct questions, the verb is moved to before the subject. Normal word order in a statement is Du förstår. 'You understand'. To turn it into a question, we put the verb before the subject and get Förstår du?
It's the same in questions that have a question word in them, like var 'where', vem 'who' etc.
Statement: Jag bor här 'I live here' – question: Var bor du? 'Where do you live?' – the verb goes before the subject.
Ja, det förstår jag is not a good answer to this question, but Ja det gör jag would be. I wrote about that structure in a comment here: https://www.duolingo.com/comment/5944292
Why is this not förstår svenska du? All other questions seem to have the subject last
Hmm... Not quite sure your observation is right. What other question have you seen with the subject last?