The correct answers are I have been studying for my biology exam for three hours. and I've been reading this same chapter since 2 PM.

Use the Present Perfect Continuous (have/has been + verb-ing) for actions that started in the past and are still continuing.

"I have been knowing" is incorrect because know is a stative verb (it describes a state, not an action) and is rarely used in continuous tenses. We should say "I have known."

"I am studying... since morning" is incorrect because the Present Continuous cannot be used with since to show duration; you must use a perfect tense.