Create the buttons and text elements that you'll need for the full joke.
Think up your best Knock Knock jokes (or find some on the internet.) Then, create one array that holds the response to "Whose There?" and one array that holds the punchlines. (Hint: The name and the punchline that go together should have the same index location in the two different arrays)
When the page is loaded, have all of the buttons and text disappear except for the title and the, "Click here for a joke!" button.
When the "Click here for a joke!" button is clicked have the "knock knock" text appear, then after one second, have the "Whose There?" button show up.
When the "Whose There?" button is clicked, create a function that chooses one of the names from the name array at random. Then, print that name on the screen and have the "___ Who?" button show up.
When you click the "___ Who?" button, have the punchline of the joke and a button that starts a new joke appear. Make sure that the punchline matches the name!
Keep working on your project until you're happy with it. You can make it look cool, add different features, think up more jokes, etc.