A hypothesis is a statement, not a question.
Can swimmers hold their breath longer that people who don't swim ?
I have no idea. What do you think ? The hypothesis is what you think.
I see three possibilities here:
1). Swimmers can hold their breath longer that non-swimmers.
2). People who don't swim can hold their breath longer than swimmers.
3). Average swimmers and average non-swimmers can generally hold their breath for the same length of time.
These are three possible hypotheses. There may be others that I didn't think of.
What do you think ? Once you decide what YOU think, you have a hypothesis. Your next job is to set up some kind of test or experiment to find out whether your hypothesis is true or not.