Observation and experimentation. We can’t do anything with black holes, but we can do lots of stuff with light and solid matter of all sorts of different types. We do tons of experiments with what we have to learn all of its properties, and then we observe how it acts differently around a black hole. Similarly, while we can’t bring a star into a laboratory to experiment with it, we’ve observed *lots* of them, very closely, at every stage of development, and come to a pretty solid understanding of how they work, so, similarly when we observe what happens to them near black holes we learn all sorts of stuff.
Then we take all that data and use, as u/suwampert said, math. The data gives us points to base the math off of, and then we use the math to predict and hypothesize(in fact, when we were learning about stars and gravity the math actually told us black holes were there before we ever actually observed them, and then they proved to be real, and over and over again since they do what we expect them to[usually]), and then parts of our predictions and hypotheses either prove true or don’t as we make further observations and do further experiments with things like vacuum chambers and particle accelerators.
Latest Answers