Three types of knowledge

Q: According to the following narration, can you explain the different type of knowledge?

Sayyiduna Abdullah ibn ‘Umar (radiyallahu ‘anhu) says: “Knowledge is of three types; the clear book [Quraan], an established Sunnah, and saying ‘I do not know’.”

Fidyah for qadha salaah

Q: My father has willed for us to pay fidyah for his qaza namaazes. We live in the US but also have a house and wheat fields in Pakistan.

1. Can we give his fida in Pakistan or do we have to give it in the US?

2. He has about 50 years of qaza namaazes and the rate per namaz is 1.6kg wheat?

3. Who should be given the fidyaa?