Learning the notes on any staff is a lot of memorization at first. There are a lot of little tricks to remember what each line and space is on the staff, but it can be a lot to learn at once. I've taught a few younger kids how to read the treble and bass clef (not any teenagers though) and while FACE and Every Good Boy Does Fine helps some it confuses others.
Make sure that he understands the basics of notes on the staff in general like there are 7 letter named notes (A, B, C, D, E, F, and G) and going up on the staff goes to the next letter name and going down goes to the previous letter name.
One method that I found worked well is to get them familiar with one note on the staff and then if they remember that note they can figure out any note. In the treble clef, the G on the second line is very easy to remember because the treble clef look a little like a G and that line is where the treble clef curls inward. If he can remember that note and remember the basics of how going up and down on the staff affects the letter name he can figure out any note. When he gets familiar and can remember the G on the staff, then he can move on to memorizing a different note on the staff. Eventually with repetition and time he will learn what each line and space on the staff is.
There are also several online sites that have exercises to train recognizing notes on the staff. MusicTheory.net has a very good exercise for it and lessons to go along with it if he is still confused. I recommend pointing him to that for extra practice in recognizing notes.