How many segments a process can have in operating system employing Segmentation for memory management
A process can only access 6 segments simultaneously through CS, SS, DS, ES, FS, and GS registers on an x86 and x86-64 machines.

These registers point to an entry in the segment descriptor table that the operating system manages. If OS uses a multi-segment memory model then that table can have an arbitrary size thus allowing a process to access a theoretically unlimited number of segments. (Intel 64 and IA-32 Architectures
Software Developer’s Manual 3-6 Vol.3)