Can you contribute to Public Loan Forgiveness (US) while pursuing a funded Masters/PhD?
My understanding is that you can only participate in PSLF when you are required to make a payment; as at least a half-time graduate student, regardless of your employment at the time, you are not required to make a payment, so you cannot participate.

Source: https://studentaid.ed.gov/sa/repay-loans/forgiveness-cancellation/public-service#qualifying-payment

Student aid reps at your institution might be a better source for clarification on this; perhaps you can declare yourself not a student for the purpose of your undergraduate/JD loans, and begin making payments? However this would also prevent you from using your student status to limit interest accrual on some of your loans.

If you have friends in tax/financial law this might be a good time to call in a favor on a 5-minute consultation.