A simple push lawnmower? They use a "magneto". A magneto is a system with a permanent magnet mounted in the flywheel of the motor and a coil mounted on the body of the motor. When the magnet spins past the coil, it generates the electrical charge for the spark.

If it is a walk behind then it probably does not have one.

Mines under the seat.

I sa a blog post on this the other day, give me 5 min to check browser history.

Most riding mowers have it under the seat. I have no idea what you have so can't help any more then that.