There is no built-in function or option on WhatsApp to let you know if someone blocks you, and you won't receive a notification if this happens.
However, there are a few ways to determine if you've been blocked on WhatsApp, so let's explore.
If only a single tick is visible after sending the message then it is an identification that you have been blocked by someone.
If you can't see the person's last seen and online status, this is an indication that you have been blocked.
If you have been following for a long time and find that there is no update on the profile picture and also there is a single tick after sending a message, then you must understand that you have been blocked.
If you are calling that person from WhatsApp, but it keeps failing everytime, then you must understand that you are blocked because WhatsApp restricts the blocked contact from calling.
If you want to add that person as a participant in the group chat, then you will get an error "can not add participant". Then it can be a strong indication.
So if all these indications are correct then you have to understand that someone has blocked you on WhatsApp.