Hi, it is understandable, but it's not as precise & clear as it could be. There are many different ways it could be worded. Consider the following options.
If speaking to an educated native speaker:
What constitutes a successful person, in your eyes?
If speaking to an unintelligent native speaker, or a non native with weak English:
What IS a successful person?
Somewhere in the middle:
What's your definition of a successful person?
Or:
What does it mean, to be a successful person?