My father has given me some cash as a gift. He has told me that he has already paid Khums on it. Am I liable to pay Khums on it again if one year has passed and I have not used it?
Bismihi ta'ala
Your father did his duty by paying khums on what was liable for him. Once he transferred that amount to you, it now becomes your responsibility. In regards to gifts and khums, this depends on taqleed, so you will need to refer to your Marja' taqleed to see if khums is liable on gifts.
And Allah knows best