I have two at home and one at the rehearsal space. They are all 8 ohm cabs. But that doesnt mean yours is. Plug a speaker cable in and check the resistance at the other end of the cable with an ohm meter. Place the meter leads on the tip and sleeve...
If you check with an ohm meter, it won't read out exactly 8 or 16 or 4. Whatever it's closest to is right - I believe 16 ohm speakers read out at like 13, 8 reads out around 6 and 4 is around 3. Going from memory so I may be off a hair, but I promise it won't be exactly 8/16/4.