my daughter is a teacher and her husband a criminal defense attorney. What can my daughter do about him hiding much of his income

During a divorce proceeding, both parties will have to go through an extensive "discovery" period, where they are both required to produce numerous financial documents including W2's, 1040s, pay stubs, bank statements, etc., for the past three years or more.  Both parties are also required to fill out what is called a "Statement of Net Worth" which details their financial situation.   If your daughter's husband does not produce these documents, then he can be ordered to the court, and held in contempt if he still refused to abide by the court order.