Within the Luxembourg Gardens looking towards the dome of the Panthéon in the background. 

The inscription at the bottom is partly cut off by the  image but it reads: "To my friend McKim John S Sargent." This was Charles Follen McKim who would form McKim, Mead and White, the architectural firm who would work with Sargent in 1890 on the Boston Public Library murals. 

It's possible that McKim met Sargent the previous year when he traveled to Paris for the Paris Exposition of 1878.