Asking a very direct question can appear rude, in some situations.
A way to make a question less direct is to ask about the question:
Can you tell me who the Prime Minister of India is?
This removes the "demand" implied by asking "Who is the PM of India?" and so makes the question politer. It requires the person listening to understand that this is just a polite indirection, and answer
"Mr Modi" or "I don't know."
Answering the question directly
"Yes, I can"
Is being a "jerk". You would be expected to understand that this is just a polite question and to answer the implied question.
Using "can" questions can also be used to make polite requests. If someone says:
Can you make me a cup of tea?
And you answer "Yes, I can", but do nothing, you are being a "jerk". A proper response would be either
Sure, do you want milk?
I can't right now, I'm really busy.