Is it permissible for an employee who works as a sales representative for a car dealership to take a commission from the insurance company if he encourages the customer to opt for their comprehensive insurance?

If the insurance company is a traditional commercial one, then enticing a customer to subscribe to it is Islamically forbidden (haram). This is considered an indication towards falsehood (batil), and the commission received by the one who directs others to subscribe is ill-gotten gain (suht) because it is in exchange for a forbidden benefit. The employee must work for the benefit of their employer, not for their own benefit.