Best settings on Dslr for dawn, christmas lights and fireworks?

Camera: Nikon D3300

Rainy and water conon

Automatic (Auto)

Depends what you want.

Freeze action, then fast shutter. No motion and sharp/crisp, then slow shutter on a tripod. We don't know sort of shots you want.

Your camera has a nice LCD and a good lightmeter.

Use the lightmeter to get a good approximation of the best exposure and then make the necessary changes using what you see on the LCD. You can fine tune the exposure by looking at the Histogram which you can display on the LCD.

When shooting at dawn and dusk, while a tripod is recommended, you can probably hand hold the camera.

Christmas lights will require longer shutter speeds like 1/15th second or longer

Fireworks will require you to use the bulb setting on the camera and hold the shutter open for at least three air bursts. You will have to adjust the lens aperture so that the fireworks are not overexposed. I start at f/11 and close the aperture from their by using the LCD on the camera. You will need a tripod for this and a remote shutter release will also be beneficial.

In all cases use ISO 100 or ISO 200 to prevent noise in your shots

There are none, that's why your camera is adjustable.

Too many people don't realise that buying a, "Cannonornikon," can't magically transform them into photographers, and that they have to learn how to get the best out of their cameras.

Without knowing anything about photography, your best chance to be lucky is Auto. If you want to learn, search for sites in the internet about how to shoot those scenes and experiment. There's no one setting to shoot them all. You will always have to adjust to get it right in every situation.

Use manual. Use these as start points and adjust to get the effect you want.
Dawn - underexpose by 1-2 stops from whatever your camera meter tells you.
Christmas lights - underexpose by 2-3 stops from whatever your camera meter tells you. Set white balance to tungsten and increase colour saturation.
Fireworks (assuming you mean air-bursts) - open the aperture to max. Manual focus on where you expect the firework burst to be. Shutter speed to B. Hold it open until there's a burst then close it. If over 10 secs, abandon the shot.

Don' t use auto. Use manual and a tripod for best results. You will need a slow shutter speed, so you will get camera shake if you try to hand hold it. Also don't use flash.

Addressing Christmas lights. I set my aperture at f/10 because that's about the sweet spot of a lens and let the camera decide the exposure time.