A debt consolidation loan can actually come from a few different sources. Essentially, a debt consolidation loan is just a fancy way of saying that you are taking out a loan and that you are going to use the money you get when you do so to pay off a bunch of older debts so you'll only have one lender and one payment to make. Many people will get personal loans, use credit card balance transfer offers, or even tap into the equity in their houses to consolidate their debts. There are also some specific loans called "debt consolidation loans" that are targeted for the purpose of consolidating debt, although those usually aren't a great idea because they often have higher interest rates and less favorable terms than standard personal loans.
In any case, no matter what type of debt consolidation loan you take, whether or not you need a co signer is going to depend on whether you can qualify for the loan on your own or not. If you have a reliable source of income and good to fair credit, you can probably qualify for some kind of consolidation loan on your own - especially if you use your home equity or take a special debt consolidation loan. If your credit is very poor and/or you don't make enough money to convince the lender you have the resources to pay back the loan, then you may be told by your lender that you will need a co-signer.
In any event, before taking any debt consolidation loan, you need to consult with an experienced lawyer for help and advice to find out if the loan really is in your best interests or not.