Can a Schengen visa holder enter Turkey?

No,Turkey is not part of the Schengen Area. Schengen visas are not valid.

Technically speaking, it is unclear whether or not the Schengen VISA holder can enter Turkey or not. It would depend on the passport the VISA holder has and whether or not that person can get additional VISAs. What is clear is that a Schengen VISA is not valid itself for entry to Turkey.