If your wages are being garnished, filing bankruptcy can stop the garnishment immediately through the automatic stay.
Garnishment limit: 25% of disposable earnings or amount exceeding 30x federal minimum wage
Garnishment requires a court judgment (except for taxes, child support, and student loans). Once a creditor has a judgment, they can instruct your employer to withhold a portion of your wages.
In some cases, yes. If wages were garnished within 90 days before filing, the trustee may be able to recover them as a "preference payment." This is more likely in Chapter 7 cases with a no-asset designation.
The automatic stay takes effect the moment your petition is filed. Most employers stop withholding within 1-2 pay cycles after receiving notice.
No. Child support and alimony withholding continue during bankruptcy. These debts are not dischargeable.