What's the difference between “have you seen?” and “have you ever seen?”

 Ever means 'at any time'.

So,

“Have you seen?” is said when you are asking someone if they have seen a particular person or thing in a specified short period of time maybe this hour or this day.

While, “have you ever seen?” is spoken when you are asking someone if they have seen a particular person or thing at any time maybe even once in their whole life.

For example:

• Have you seen Claire? I thought she was waiting for me at the bus stop.

• Have you ever seen a flying UFO? I thought they only exist in fiction.

• Have you seen my dog? I am looking for him for the past hour!

• Have you ever seen my dog? He's really cute!

from: https://english.stackexchange.com/questions/502746/whats-the-difference-between-have-you-seen-and-have-you-ever-seen