Salve Dacice,
You may want to go back and reread the explanations on indirect questions. The indirect question uses the interrogative rather than the relative pronoun because the part of the sentence in the subjunctive is actually a question.
In the sentence
Nunc scio quid sit amor, the
statement is
Nunc scio "Now I know" and the
question is
Quid est amor? "What is love?". When you wish to combine them into one sentence, the question portion of the sentence must be put into the subjunctive (i.e. change
est to
sit).
Also, take note that Wheelock specifically says in the second paragraph on page 204:
Wheelock's Latin wrote:The subjunctive in an indirect question is usually translated as though it were an indicative in the same tense (i.e. without any auxiliary [verbs] such as "may" or "might").
Pay attention to how these sentences are translated in the examples. According to this rule, the indirect question
Nunc scio quid sit amor should be translated "Now I know what
is love" or, more properly, "Now I know what love is", without any words such as "may" or "might".
Be well
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae