You need to look at the garnishment paperwork. If it is not on there, then you need to call the court that ordered the garnishment.

I found the following "Seventy five percent (75%) of all earnings for personal or professional services earned during the last ninety (90) days shall be exempt from garnishment except for collection of child support obligations." at 12 OS Section 1171

I also found the same information at: http://www.bcsalliance.com/debt1_oklahoma.html