what is the amplitude of quantization levels?
Practically speaking an 8-bit linear PCM encoder is implemented inside an 8-bit ADC (Analog to Digital Converter). Such an encoder accepts an analog input within a given refence voltage range and divides this range into 256 equally spaced quantization levels. Some minor deviations may occur based on the quantizer level distributions especially at the first and last levels. 

At this stage analog input is converted into a PCM bit stream consisting of 8 bits of quantization codes per each sample. 

Now to view these codes ? you can use a binary analyser to see each bit on or off in parallel... 

Or if you mean observing the output of a DAC (Digital to Analog Converter) driven by this bit stream then you will be converting these bits back into analog and view it using the oscilloscope. The values will be steppy and be scaled by a reference voltage.