I found 2 sources for COULDST THOU BUT KNOW:

Famous Songs, Volume 3, edited by Henry Edward Krehbiel (Cincinnati: John Church Company, 1902), page 10, has an arrangement for one voice and piano. It has one verse in French, beginning "Veux tu mon nom?" and a verse in English, beginning "O wilt thou share an honored name...?" The title is given as SI TU SAVAIS (COULDST THOU BUT KNOW).

Gems of Foreign Song (Boston: White, Smith & Company, 1881), page 120, has the French words plus English words by J. C. D. Parker, beginning with "Wouldst have my name? It is for thee."