1. On top of indicates a position higher than the object.
Pattern: verb + on top of + noun
They put the blanket on top of the sheets, and the bedspread on top of the blanket.
I�m sure I left my keys on top of the desk.
2. Expression
to be on top of something�to be sure about one's knowledge or control of something Her son had a hard time learning math, but he is on top of it now.
Rules to play Triathlon
Knowledge of Course
The sole responsibility of knowing and following the prescribed cycling course rests with each participant. No adjustments in times or results shall be made for participants who fail to follow the proper course for any reason whatsoever.