Answer:
Domain: all real numbers
Explanation:
This graph is a parabola. It's equation looks like it should be:
y = x^2 - 1
If you have a graph and are looking for the domain, you are determining where the graph exists. For what x's the graph exists. If you have the equation then the domain is what x's may be put into the equation. There are no limitations on what numbers can go into this equation so the domain is all real numbers.
There are several ways to write the domain is all real numbers, set builder notation and interval notation. But the main idea is that it is all real numbers.