Some comedians write their own material, while many if not all comedians have writers.
Bob Hope, for instance, had a stable of writers working overtime. Same with most renowned comedy players, for standup, tv, radio, movies, etc. Was it Milton Berle who said, " I never heard a good joke that I didn't want to steal."? Probably not, but then again.....
Yes, Dane Cook writes his own jokes, as most comedians do.
Yes, they write their own material.
Yes, they write a lot of their own material. They are very talented musicians.
Every day life or people who write for us
Most stand up comedians get their start through local comedy clubs in their city. If their material is good enough, they can be scouted by major networks, such as Comedy Central, to do official specials.
A heckle of comedians
youtube mostly or they have their own websites where you can watch their old performances
No, only the creator can copyright material. You would be writing fanfiction, which cannot be published or sold.
The Comedians in Africa was created in 1967.
The Comedians - novel - was created in 1966.
The Comedians of Comedy was created in 2005.
Creative means you have your own individual style and "voice" when you write. You learn how to be more creative by reading what other writers have written and then trying to write your own material. The more you read and the more you practice, the more original you'll become.