In Greek, when you want to say "I have nothing", "I have never heard" etc you use double negative. Δεν έχω τίποτα and δεν έχω ακούσει ποτε. So "have you never heard this?" Is "δεν το έχεις ακούσει ποτέ (σου) αυτό;" which could also be translated as "haven't you ever heard this?" (For the "have you never heard of it?" which implies surprise I believe, you emphasize ποτέ when speaking)
Το έχεις ακούσει ποτέ (αυτό); can be translated into English as Have you ever heard it? with or without αυτό, which is there for emphasis. One may add αυτό when being really surprised by "what they heard/saw", or point to something while saying the word αυτό, to clarify what the question is about.
Disclaimer: I am not a native Greek speaker, although I am pretty confident about what I wrote.
Ever is necessary here because we have "Ποτέ" in the original sentence. Ποτέ means never in negative statements (Δεν τρώω ποτέ ψάρι =I never eat fish) and ever in other situations (Τρώω ποτέ ψάρι; =Do I ever eat fish?). It is also common to phrase the sentence above as "Το έχεις ακούσει ποτέ σου αυτό;". Ποτέ σου is more emphatic and actually points to personal experience asking about "your (ever) lifetime" experiences.