In the lesson, you have to scroll way down, and then keep on scrolling. When you get to the area that has a wide yellow / gold bar that says "MARK AS COMPLETE" look below that and on the right side there is a button that says "PRINT NOTATION". That's what you are looking for. It's a little weird because there are two or three places that make you think you can print, and when you try to print nothing happens. Look for the PRINT NOTATION button. That's what you want.

Note also that due to licensing restrictions you will not be able to print notation on a lot of song lessons. You can print for the songs taught in the fundamentals courses because those are either public domain (e.g., Ode to Joy)) or writtten by the instructors (a lot of Lisa McC's).