Is there a specific prayer or supplication for seeing the deceased in a dream and knowing their condition?

There is no specific prayer or supplication found for seeing the deceased in a dream. What is more important is to supplicate for the deceased and give charity on their behalf. Not seeing the deceased in a dream does not indicate their bad state. The dream might also be from Satan, who can appear in forms other than that of the Prophet, peace and blessings be upon him.