Fighter’s “Know Thy Enemy” let’s players learn the target’s level. Where’s that information located?

@JeremyECrawford Fighter's "Know Thy Enemy" let's players learn the target's fighter/ class level. Where's that information located?

— Step 5 SSQ Qualifier (@fartboss) May 2, 2017

Know Thy Enemy says "if any" after "levels" since there's a good chance the target doesn't have levels, which is true of most monsters. #DnD https://t.co/URgbZtDqPQ

— Jeremy Crawford (@JeremyECrawford) May 3, 2017