Which one Is the guaranshee? The collector or the debtor? Thank you

The debtor

Neither.

Typically, the debtor (the person who owes the debt) is sued by the creditor (the person to whom the debt is owed).

The creditor gets a judgment.

The creditor gets a writ of garnishment from the clerk of court.

This writ of garnishment is served on a third person, usually the debtor's employer or the bank in which the debtor has funds deposited.

The entity upon which the writ was served is the "garnishee". Or perhaps the term might be used to describe the judgment debtor. But it would not be the judgment creditor (or a debt collector acting in the creditor's behalf).