How can I know if my home has soffit vents
That's unvented soffit. The vented variety has a pattern of slots punched into it on the flats.  My guess is that there's plywood underneath, and it wasn't deemed necessary to open it up before covering it with maintenance-free aluminum soffit. 

You may be able to do this to get venting in place:


Remove the aluminum soffit by detaching the fascia and pulling the nails along the bottom edge that secure the soffit panels. 
Cut a channel in the original wood soffit. Whatever you can conveniently remove with a circular saw will probably be adequate. It's a messy, gritty, upside-down job, so have some eye and respiratory protection on hand. 
Reinstall the aluminum soffit and fascia, but replace every other panel with vented soffit. You could also use all vented panels, or the variety that's partially vented. Since you (presumably) don't have taller energy heels on your rafters, that'll be plenty of vent area.
In the attic, install vent baffles. These create a channel up over the wall plate and along the roof sheathing, past the level of the insulation. 
Install additional vents near the ridge to meet modern standards based on attic area. Do not install gable vents or vents lower on the roof. You want as complete an airflow path along the roof as possible. 


Note that this would need to be done on eaves (at wall level), but not on rakes (on gable ends). 

As a lower-cost (but somewhat less effective) solution, Use a hole saw to cut through both the aluminum and plywood soffits, then install round louvers every 6-12 inches.