My wife and I live in Pennsylvania. Acouple of years ago a judgement was brought against a party who had stolen monetary assests from my wife's father. The party pleaded guilty nad was ordered to pay in monthly payments. He has not done so in 3 months. What can we do?

Is it being paid though the court, ( if so they are aware of it) but you report it to the court clerk that the payments are not being made ( I assume this was though criminal court) not a civil court judgement.

Yes. It appears to be a resitution order, not a civil judgment. Inform the prosecuting attorney &/or the defendant's parole officer.