ANSWER:

You must tell him that this is prohibited in Islam and that the income is haram.

You must not assist him in anything and you will sinful as he is if you do. 

My father runs a tobacco store, selling cigars, cigarettes and the like. He wishes that I take over the main store so he can expand it. He will start training me in a week on how to manage the store. I know this is haram. But, how can I tell my father this is haram? Also, if he does not listen, is it permissible that I run the store until I can sell it and donate the money to charity?