This F# note is written in the second space of the treble staff.
In Lesson 4 you learned that a sharp sign written after the bass clef at the start of a line applies to all F notes on the bass staff. Similarly, when a sharp sign is written after the treble clef, it applies to all F notes on the treble staff.
This song contains two F# notes on the treble staff, one each in bars 1 and 3.