Problem generating square wave using IC555
After the resistor (at the basis of the 2N3055) the voltage can never get more than 0.6V, which is the BE voltage of the transistor.

IMO this circuit is highly suspicious. As Dan remarks, the +/- of the coil are the wrong way round, and there is no protection for the transistor. A freewheel diode would be a bad idea as it would suppress the spark too. AFAIK a zener is a good solution.

The 555 lacks the highly recommended 100nF decoupling capacitor at pin 5.

But my main objection is the base drive of the transistor. A 2N3055 has a lousy Beta: a datahseet shows a minimum of 5 at 10A. This circuit seems to call for 6A, so at the very minimum I would calculate with a  Beta of 10, which would require 600mA base current. With the 100 Ohm resistor the base current will be ~ 10/100 = 100 mA. (Don't lower the resistor, 200 mA is the maximum for a 555).

The circuit should use a differnt transistor, or a darnington, or a FET. The next circuit on the page that you link to shows a FET. (But its high voltage protection does not look good to me.)