Is money earned from working in a leather factory permissible, knowing that the car used for commuting to this job was bought with money earned from a previous job that involved dealing with pork and alcohol?

There is no harm in your current work at the leather factory, nor in benefiting from what you earn from it. The fact that the price of your car came from money earned from a previous job in a restaurant described as having unlawful elements does not affect it.

You must seek forgiveness, repent, and resolve not to return to the unlawful. You may donate a percentage of your previously earned money, which you believe likely equals the proportion of the unlawful work, to the poor and needy. The remainder is permissible for you.

Al-Nawawi mentioned that whoever doubts the amount of unlawful money they possess should strive to donate it. Some scholars stated that whoever performs an unlawful act out of ignorance may benefit from what they earned. As for one who knows it is unlawful, they should dispose of it through charity or similar means. And Allah knows best.