There is no way of making CLKOUT frequency different from CPU.
For example If CPU is at 48MHZ, CLKOUT can not give an output of 12 or 24 MHZ.
Register CPUCS can change CPU speed to 24 and 48MHz. CLKOUT speed changes with CPU speed. This can be seen in Figure 6-1, 6-2 and 6-3 of Technical Reference Manual.
Timers can be used to implement the frequency required. Timer Frequency will have the following charateristics:
1. The clock can be of maximum frequency 12 Mhz, as the input to the Timer module is CLKOUT/4 or CLKOUT/12.
2. The clock produced is of 25% duty cycle.
3. There is a little lag w.r.t. the CLKOUT signal.