Measure power output without oscilloscope

Good one. Five hours early. But still, give the man an A for effort.

Check ur calendar.  

What, exactly is the purpose?

How are you going to measure the power output?

Power can be either peak or average. Relationship between them depends on the shape of the signal. For sinewaves average is a half of the peak power. Knowing peak power (peak voltage squared over speaker impedance) will let you calculate average power - a very useful thing if you listen to sinewaves.