The short answer to the title question is everywhere. We are all conscious of it where competition directly impacts on us, but don't always understand the full breadth of it.
Guy Gilchrist used to write a column for The Rider, a horse newspaper I work for. He wrote of business concerns from the perspective of people in the horse trade. He raised the question of where they saw their competition and learned that the first response is the next horse business down the road. Obviously there is some truth to that, but it is only part of the answer. The bigger answer that Guy pointed out would include golfing and boating. In other words while you are competing against those in the same type of business, you are also competing against a wider group of people and in some ways you have more in common with your supposed competitors than you do with the outsiders.
Competition can come from all sorts of directions. I remember working a booth at a pet show where we had an excellent location right by the main entrance. We had an excellent product, a pet cleaner/deodourizer that I think was one of the best products I have ever sold. However one thing was overlooked. Closer than us to the entrance was the ice cream vendor. I remember one man coming in with his wife and four kids and decided it might keep his kids quiet if he bought them all ice cream. We were the first actual "booth" he visited and he was impressed with what we offered. Unfortunately when we got to the price he realized he didn't have enough left--the ice cream man had gotten it!
You as a consumer have an endless desire for all sorts of things, but most of us have a limit to our resources. Most of us have to make a living so we can handle our needs and wants. So we are competing with others to make money while many others are competing to get our attention and our money.
Still another experience. Visiting a factory that made chairs when a spokesman asked my group (who sold office supplies and furniture) who we thought our competition was. We could all think of other office supply competitors, but he expanded our thinking to include computers. We initially protested that we didn't sell computers. He pointed out that one of the first things a new company bought was a computer, then they would buy a big impressive desk and chair for the boss and finally with what budget was left they would think about throwing in a few things like a chair for their secretary. His point was that the whole business literally fell on the pelvis of the secretary. I thought he was exaggerating a bit, but within the year two owners begged our office to supply an upgraded chair before they lost another secretary.
We all are trying to sell something. If we are going to make an honest living it has to be something with some perceived value. If we are going to survive and prosper we have to make sure our prospects realize the value of the solution we are offering. Getting attention is important and offering value to the right people. The prospect has priorities, but often doesn't think of the details.
When you understand your competition you will understand your prospects a little better. Each person has their own set of wants and needs and when you understand the most basic needs you will have a competitive edge.