Upvote:1
Transit visa is not required if your friend is not taking a domestic flight in India to reach his final destination - for e.g. if your friend's flight has a flight from Delhi to Mumbai - he would need to apply for a transit visa.
Your friend can stay in the waiting area for international passengers in case he is not taking a domestic flight to complete his journey.
Transit visa canbe applied with Indian high commission from Singapore in this case.