This is not a nose. Like all whales, dolphins breathe through a blow-hole in the top of their heads. They have tiny ears, which they probably use only when their heads are out of the water. Their underwater acoustic sense and echo-location skills are legendary. The sound-generation within the bulbous foreheads is sophisticated enough to give them a clear picture of their surroundings.
Dolphins are mammals and as such are warm-blooded and bear live young, which they suckle.
A dolphin is a mammal and as such needs fresh water, which it gets from the fish it eats by swallowing them whole, using its teeth merely for gripping. Inevitably it takes in a gulp of seawater with its lunging bite, so the rear of the mouth is used to eject the seawater squashed up by its tongue. Perhaps we have an affinity with dolphins because they breathe air like us and spend a lot of time swimming near the surface. Alone among sea-dwellers, it is whales and dolphins which reveal their presence when they breathe. Because of this, they were a lot less mysterious to ancient peoples than other creatures of the deep, and healing powers were attributed to them.