It may seem confusing, but in the spark circuit, we have the spark when we try to turn off (cut the current) the primary winding. By cutting off the current from the primary winding, the transformer creates a back EMF with a very high voltage in the secondary winding and that creates the spark.
So if we want to check the spark, just connect a dc voltage to the primary winding and then disconnect it. Just by disconnecting the dc from primary, you will see the spark. Take caution. If you don't put a reverse-biased diode in parallel to the primary winding, you will see a spark there too; and if you are touching the wires while disconnecting, you make get an electric shock too!
Now let's get to your circuit. The circuit uses the positive voltage on the 'Excuter coil' to charge the primary winding. Mostly just when the voltage is at its peak, the 'pulse rotor' coil will trigger the SCR. By triggering the SCR, the voltage around the primary winding will drop and the back EMF will create a spark in output. When the 'Executor coil' creates a negative voltage, SCR will reset and you can repeat the procedure.