It would really be pointless to look at CPU registers from the shell level. By the time you saw the values, they would have changed a gzillion times. If you are talking about seeing the values of memory mapped IO registers, or IO-space registers of x86 CPUs, then you should be able to write a simple program that uses the /dev/mem or /dev/port facility, and call it from a shell commandline. That would require root privileges.
A debugger such as gdb will expose such data as moo-cow has already pointed out.