It depends on whether the loan is paid off. A buyer needs to know the car is yours to sell, and a loan recorded on the title means the lender still has a claim on it.
If you paid it off
Your lender’s release of its claim is the paper that matters. With it, you can get a replacement title if you need one, or sign your state’s form for selling without a title where your state allows it. Nearly every way round a missing title requires that no loan is recorded on the car.
If the loan is still open
The lender usually holds the title, so the sale has to go through them. Ask your lender what they need before you list the car.
Tell your buyer
If there is a loan on the car, or there was one recently, say so in a message to your buyer before you take their bid, and ask what they need from you on pickup day.
Read Can I sell my car without a title? for the rest of the paperwork.