Facebook does not send any specific notification to inform you if someone has denied your friend request.
When you send a friend request to someone on Facebook, they have the option to either accept or decline it. If they choose to accept your request, you will receive a notification confirming that they have become your friend. On the other hand, if they ignore or decline your request, you won't receive any notification indicating this.
There might be some indirect ways to infer if someone has denied your friend request. For example, if you visit their profile and the "Add Friend" button is still visible, it could suggest that they haven't accepted your request. However, it could also mean that they simply haven't seen or responded to your request yet.
Remember, Facebook's features and notifications may change over time, so it's always a good idea to check Facebook's official help center or community guidelines for the most up-to-date information on their platform.