Sorry, I can't help you identify the oscilloscope.
Can you say why you need to change the potentiometer?
It is common in old oscilloscopes with controls that have not been used for a while to get dirty and electrically noisy. Often all that is required is to spray it with a contact cleaner and work the switch or knob back and forth for a few minutes. After cleaning I then spray a tiny amount of potentiometer cleaner into it (similar to contact cleaner but also has a lubricant).
If you do still need to change it the hardest part will be determining what the replacement part is. The parameters include size, shaft length, shaft kind, resistance, taper,....