The reason why scientists know most things is because they carry out research and dedicate their time to find solutions. However, in the case of Bill Nye the Science Guy his knowledge comes from books and TV scripts.
In fact, it's usually the case that as a scientist gains more knowledge within a single field of study - they know less outside that field. This is just due to the fact that, to get really good in a single field of scientific study, you have to devote so much time to that field that you don't have time to study other fields.
Bill nye is dead btw and scientist dont know everything. They only know like .0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000...etc.01% of the facts of life, matter, science, death...etc. We actually barley know anything we will forever be learning and pass aroung the knowledge until we dont exist.
Scientists know a lot by educating themselves. You can educate yourself by going to college, and completing the required schoolwork. If you are still in high school, you can educate yourself by completing your homework and asking questions :)
They make a lot of preposterous theories that people of like belief accept as truth, example, Richard Dawkins said that life looks overwhelmingly like it was created, but we must remember that it evolved. In the forward of the centennial edition of Darwins" Origin of species", W.R. Thompson writes, the evidence of evolution is unsatisfactory and doesnt support a conclusion, So when science puts forth theories on evolution, the conclusion is its their opinion, nothing else.