How does one find the vocabulary you are supposed to know for a given lesson or are you just supposed to guess it then do it again after you have got it wrong
Seems to me that it would be logical to be given the vocab before the lesson starts
You guess from context, or you can hover over the word with your cursor and it will define it for you.
if you mouse-over the words you don't know you will see a translation
Another way to learn the words is to use Tinycards. It is the matching words for the lessons in flash cards. I used it for quite a while but then stopped because it is actually harder to remember the words, I found, than figure them out in context, which Duolingo provides. However, I did finish the French section and it did help a lot.
Are you asking about the questions that show up with a picture and ask you to translate a word into your target language before it's been introduced to you?
(I assume the question ordering allowing this reflects a bug.)