Q: Engine Light is blinking, car shakes, and gas cap light is on

For the case of the gas cap leak you will need to have a smoke test and cap test done to see where the evaporative system is leaking. In order to do this will require the system put in test mode or the vent will stay open and may be thought to be a leak. For the misfire you will need to have a computer scan done to get the cylinder that is misfiring and check the coil and plug for that cylinder and replace parts as needed or additional diagnosis will need to be done.