"Perhaps you know the books."
Translation:Fortasse libros scitis.
It seems like the English here should differentiate between 2nd singular and 2nd plural. I imagine the hovertext does, but (I don't look at that unless I have to, and), a first glance at the English doesn't indicate whether the verb is singular or plural. Did anyone else have this issue, or is this just me?
Are you suggesting that that scitis is the wrong verb here? Is Latin like French, which has the two verbs savoir and connaître meaning to know, and Spanish, in which the equivalents are saber and conocer? If so, should scitis be cognoscitis, or is that not the correct Latin verb?
Yes, that's what I'm suggesting. Scīre suggests knowledge of a fact ("You know that the books are in the forum": Scītis librōs in forō esse, a so-called indirect statement, not taught (so far) in Duolingo).
Nōscere and cognōscere, esp. in the perfect tense, are used for knowing (a person, a place); being familiar with particular books is in this category. I would use the perfect tense of these verbs, since the present tense means "learn, come to know, become familiar with," so I'd use nōvistis or cognōvistis in this sentence.