Can swimmers hold their breath longer that people who don't swim. what is the hypothesis?

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.