Identify the determiners in the following sentence: I knew his father who was an honest man.

Determiners are words such as the, my, this, some which are used before nouns.
Determiners include the following common types:

Articles: a, an, the
Demonstratives: this, that, these, those
Possessives: my, your, his, her etc.
Quantifiers: some, many, few, one, two etc.

Source: Cambridge Dictionary.

So, the correct answer: ক) his, an