Is it possible to know about the research quality of a professor from the number of citations of his/her papers in Google Scholar?
This would vary by field, of course. But there is more to selecting a good advisor than just their output, even the recognized quality of that output. In fact, having a superstar as an advisor can be a mixed blessing/curse. They may be so focused on their own research and career that they give you little direction in your own. If you are especially self motivated and can find and develop your own research this is less of an issue than if you are like most students, needing guidance in finding problems and developing solutions. 

But the citation count of a person gives some, but not the final, measure of their quality as a researcher, not necessarily as an advisor. If you want an even better measure (IMO) get the citation count of the students that they have advised. Even just the number of "produced" students and where they wound up in their careers is a good, but not perfect, measure. It is more likely to be useful for a senior professor than a junior one, of course. 

If you are already at the institution, student scuttlebutt is actually a pretty good indicator of an advisors "quality" as an advisor, if not as a scholar.