This is an excerpt from Minuet by Boccherini from John Thompson's Grade 3:
Is the grace note in the 3rd measure played concurrently with the E on the bass line, or just before it?
This, like every other piece in "John Thompson's Grade 3," is a pedagogical arrangement, meaning it differs significantly from the original music.
The original version of this piece (see page 20) is actually notated without gracenotes, but with a trill on the first A. This would be interpreted as what we now call two gracenotes ahead of the A, as seen here. This indeed matches what you will hear professionals do on recording.
However, that's not how you should play John Thompson's Grade 3 arrangement. That arrangement was written to conform to modern notational practices, so "baroque gracenote interpretation" does not apply. Modern interpretation of gracenotes is to play them just before the beat, with the following "big" note occurring in its regular metric location. (In other words, the specific gracenote you mention should occur just before the E in the bass.)
Practice this passage by playing it accurately and in-time without the gracenote; then add the gracenote later without changing the time of the notes you're already playing.
I'd love to hear from a scholar better versed in interpretation of Baroque music; my (very limited) expertise in this piece specifically is from several youtube videos of string quartets performing this minuet.
That said, the grace note appears to come ahead of the beat. I would encourage you to listen to several interpretations of the music by string quartets to get a feel for the right rhythm for that entire 5-note figure (grace note + 4 sixteenth notes).