should work, but try double quotes
Data <- read.csv("/Users/mopopo/Desktop/Econ5370/ps1_q2.csv",header=TRUE)
(Don't use lower case data, because that's the name of a function. Same with df, although you can often get away with it. And it's good practice to put a space before an after operators, such as <- .)
Better yet
install packages("readr")
and
Data <- read_csv("/Users/mopopo/Desktop/Econ5370/ps1_q2.csv")
which does a generally better job of assigning the correct variable type.