An easy way, without getting into OBD2 and apps, is to do a test drive of over 50 miles and be sure the battery is fully charged at the start.
Check the 'Energy Usage' page to be sure.
You want your drive to use at least 50% of the capacity to make the results more accurate.
Check the page again at the end.
You're looking for
kWh used and the
percentage of charge.
Run the math.
2014 Spark EV had a slightly higher rating than the following years due to changing the cell supplier.
Somehow the EPA rating remained the same....
'14 was ~19kWh
'15 and '16 was slightly less.
Bolts don't give you that number directly on the screen, so it's easy on the Spark.
You can find lots of info on this forum about typical kWh numbers for used Spark EV's.
I haven't logged my numbers in a while, but my '14 is doing great at 97k miles.
It still displays ~73 miles of range on the GOM. But the GOM uses driving history. My usage is usually 80% ~70 mph driving with the AC on.
Good luck. Post your results. Hope it's a bargain Spark EV because the 8 year warranty is coming up.....

'14 Spark EV 2LT w/ DCFC. 97k miles !! Going strong!
'17 Bolt Premier w/ It All! 75k miles. Brand New Pack w/Warranty!
GM needs Modern Troubleshooting tools for Modern EV's.
3 step Trouble Tree, 1st try, nope, 2nd try / cost $800. 3rd try fixed it.