Please, read the documentation: http://www.cplusplus.com/reference/cstdio/fscanf/
As you see, fscanf is declared in the <cstdio> (in C++, or stdio.h for C) header.
fscan_s is not part of the standard. It's implemented by Microsoft (see documentation) so OnlineGDB doesn't recognise it.
Therefore, the second part of the question (which C++ supports it) is invalid, as, again, the standard does not support it, it's only available on Microsoft operating systems. (OnlineGDB is not one of them.) Specifically on Microsoft platform, I'd assume, all C++ versions would support it, but again, only on their platforms.