A Power of Attorney is not filed with any type of court. You must track it down through your family members or through the attorney which prepared it for your father. If you can’t find a copy or if you weren’t named as a successor attorney in fact, the easiest thing to do is to have your father execute a new Power of Attorney, if he is still competent. If your father is no longer competent, then you will need to start a guardianship and/or conservatorship for him via the court system.