What information does the pandit need before performing the ritual?

The pandit needs: (1) Full name of the departed person, (2) Gotra — your family’s Vedic lineage (if unknown, use Kashyap), (3) Date of death (approximate tithi or calendar date is fine), (4) Relationship of the performer to the deceased (son, daughter, grandson, etc.), (5) The specific rite to be performed. For Asthi Visarjan, no additional information is needed beyond the above. For Tripindi Shradh or Narayan Bali, additional details about the circumstances of death may be required.