Any field of thought has fundamentals, the bedrock it's built on.
Under that is the tectonic plate, the question too obvious to ask: does this exist?
For most fields that's obvious. Physics doesn't need to be checked. Biology is obvious.
Metaphysics ... it seems likely.

Does consciousness exist?

The study of consciousness is unique in that it only exists subjectively. Everyone feels self-aware, but there doesn't seem to be any manifestation in the objective world.
I suspect that there is, and I suspect that when we understand this better we'll realize that almost everything we assume is part of the objective world is in some way mediated or caused by consciousness.
But for now I think we should demonstrate that consciousness exists, because there are people who deny this, and because it's nice to know what we're dealing with. It may even provide us with clues to understanding it.
We need to look for things which are evidence of consciousness, things we can accept even if we don't understand the underlying mechanism.

Are there such things?
It's pretty obvious that there are.
Consciousness is experience. Self-awareness means you experience yourself.

A creature which isn't conscious wouldn't have experiences. I'm not sure that's possible, because it may be that all living things experience the world and themselves.
Simple creatures appear to have pleasant and unpleasant experiences. Most creatures avoid being damaged because they'd find that unpleasant. I assume there's a level of complexity below which this doesn't happen, but I'm not sure. Individual cells don't appear to have behavior they can control. Insects don't seem to experience pain, but there's evidence that they're aware of themselves. I don't think that this is relevant to what I'm trying to figure out.

We can consider awareness to have three levels.

1. The basic one is consciousness, experiencing one's surroundings. I'm sure this will turn out to be very common in living things. There's some thought that awareness is a fundamental property of reality, and since I've come to this conclusion myself I agree with it. That means that to some extent even inanimate objects can be considered to have awareness. For reasons I won't detail here I don't think that's relevant and I don't think it's exactly correct. Awareness may crop up everywhere but rocks don't have the internal experience that dogs do.

2. Self-awareness is similar. If a creature is aware of its surroundings it's aware of itself. In a sense your environment includes your body. (I don't want to get into a discussion of the mind- body problem here.)

3.The next level is what humans have. There are other creatures, but I'm not sure there's a lot of evidence that they're mentally as complex as us. A human being is aware not only of his body but of his thoughts. Humans have experiences. Some of these are part of the physical world and some exist only in our minds.
Unlike animals - and this is a huge assumption - humans are aware of their experiences and thoughts. We consciously rate experiences as being more or less desirable. This includes thoughts and ideas.
More than even the most intelligent animals, people can choose what to think. This is the ability that makes us intelligent, and it's extremely powerful.
Being able to rate experiences, and to choose our thoughts, means we can choose experiences we like.
That only makes sense if we have experiences. A creature which did not have experiences, which was not conscious, could not choose and go after experiences.

People choose, rate and seek out experiences. We do this, and we can do this, this because we're self-aware.

We need some examples. First because you need them, and secondly because people will say that we seek out experiences for mechanistic reasons which evolved to keep us alive.
That means we need examples of things we do that don't get us a meal or help us hunt game, experiences about which it's ridiculous to say we could want them for anything but themselves.
Any argument of that type is of course ridiculous, because it's an attempt to bolster a completely ludicrous viewpoint, but it's best to deal with nonsense right away.

Examples.
There are lots of these, because we value experiences, not least the ones which exist only in our minds.
What experiences do we seek out?

Movies. They don't get us food, help us hunt, or accomplish anything. Movies are pure experience. The human race puts enormous amounts of work into them and people who make them are treated with respect. They do nothing for us and we love them.

Poetry is the same. Put words together in one way and nobody will read them. Make them rhyme, give them a beat pattern, and they're kept forever.

Books. We love them. We could be out hunting or gardening, building a bigger house, doing something to improve life, but instead we take pure experience. We're not reflexively using experience to stand in for something more valuable because we're mindless automatons, we're consciously choosing a less valuable but more appealing experience.

Alcohol. This stuff is bad for you, but we love it. It's a poison. Even if we choose things based on some arcane combination of instincts and hungers, we wouldn't do something that was bad for us. That only makes sense if we value the experience more than hard reality, and only if we have experiences.

Drugs are the same. They change the way our minds work and make us feel different. They're experiences you can't get anywhere else. If there were lions around they'd get us killed. They don't convey any benefits, even illusory ones.

Humor. Ideas are experiences. We don't mindlessly process them the way computers do, we feel them. Jokes are fragments of ideas which make us feel different for a few seconds. Laughter and humor are experiences. Laughing at the wrong time can get you killed, but that just makes it more appealing. Humor makes you feel different, in a way people like. If you think we don't have awareness and experience, try to program a computer to recognize and appreciate humor.

The best example of this, and the one I always come back to, is bubble gum. Bubble gum is great. You can blow bubbles that stick to you and get in your hair. It's endlessly appealing, irritating and delightful. There's no earthly reason to expend the resources to get it and chew it and learn to blow bubbles. When you do they last for a few seconds and make a mess. People tell you to grow up and your social standing lessens by a fraction for the next ten minutes.
Someone's going to say, "It's instinctive because it has sugar."
That's nonsense. Buy an apple with the same money. Bubble gum is only made because it's a better experience than eating an apple. Apples are good, bubble gum is ridiculous and great. It's the skydiving of food.

If anyone says consciousness doesn't exist, I always say, "It does, because I like bubble gum."

That's all the proof you need.