A writ of garnishment will stand against the wages for a certian period of time 60-90 days depending on the jurisdiction, after the employer witholds the correct percentage of the wages for the period the will answer with the amount, or known as a judgment on answer. The ne moeny will either be sent to you directly or to the court and then to you. You might call the employer to see if they have questions , that will tell you if they are witholding the money.
The process is cumbersome and confusing for employers.
Mr. Alexander is right that getting paid under the garnishment take time ... but if it's really not happening and it's the employer's fault, the law gives you great big sticks to beat them with.
An employer that simply ignores a wage garnishment order is playing with fire. They are liable to YOU, irrespective of whether they actually withheld the employee's pay.
If they are uncooperative, you will need to pursue additional remedies in court, including discovery in aid of execution and perhaps even getting a "show cause" order that would put the employer in contempt of court.