The key differences for this Pop! can be spotted on the box. The most obvious is the the trademark “TM” is missing from the DragonBall Z logo on the top of the box. The white border around the artwork of the figure on the box is also much wider on the fake than on the authentic figure.
The placement of the figure in the box is also a little higher on the fake than on the original, and you can see small discrepancies in the paint on the fake, however, there have been reports of poor paint jobs on authentic figures as well. The most reliable clues will be on the box itself.