Children go to school to acquire knowledge. [Good] What is your father by trade? [Good but antiquated] Better : What does your father do (for a living)? He traded his expensive car for a house by the sea. [Good] Do you know the reason why he did it? [Good but you don't need to say both "the reason" and "why". You can choose either and the meaning remains the same] He doesn’t sleep very much. [Good]