The following chart from the UT Arlington Library Acknowledging Sources tutorial will guide you in your decision:
What is common knowledge? This refers to facts well known by many people and verifiable in five or more sources. Examples:
If you have any doubts or questions, ask your professor or librarian.
Err on the side of caution: when in doubt, cite!
The purpose of the citation is to give credit for someone else's thoughts, words, or works, no matter in what form they come. Therefore you need to cite your sources, including personal interviews, any printed or digital media, TV and radio programs, etc. A brief list of what needs to be credited or documented is available at the OWL at Purdue.