If I was assaulted by part-owner of a gas station and he was arrested, can I sue both him and the gas station?
You can't sue the gas station. A business is not liable for the criminal acts of its owners or employees unless such criminal acts can be shown to be more or less within the scope of the work they do for the company (like suing a bar because the bouncer, who is supposed to use an appropriate amount of force, used too much force--using force is within the scope of his job) or if the business itself was used to commit the crime (e.g. sung a contracting business which was used to defraud customers by getting to pay for repairs/renovations which were never made). However, the situation you describe does not fall under either of those situations: assaulting customers is not part of running a gas station or within what an employee or owner of it does as part of running it; and the gas station business was not used to commit the assualt. You can of course sue the person who assaulted you.
Bear in mind that you can only sue for compensation for the injuries you suffered, if they are severe enough to have a long-lasting significant impact on your life (e.g. if you suffered permanent signficiant scarring, neurological damage, loss of motion, etc.); your out-of-pocket (not paid by insurance or Medicare/caid) medical bills; and lost income or earnings if injuries caused you to be unable to work. If, as we hope, you did not suffer significant injury, loss of income, or medical bills, there is little or no point in suing.