is schon mal always used together for ever?
Pretty much. It can have other uses, too.
Not a native speaker, but I'd say "Hast du je eine Girffe gesehen?" The Duolingo sentence seems to mesn "Have you seen a giraffe yet?"
"yet" would have just schon.
With the schon mal, it means something like "before" or, as here, "ever".
Hast du je(mals) eine Giraffe gesehen? is also possible -- I would prefer jemals to je here, personally.
I wrote "have you already seen a giraffe?" and for once my question is: should it be not accepted? Because it's not the same as have you ever
"Have you seen a giraffe already?" seems like an equivalent translation to me, no?
"Have you ever seen a giraffe?" is asking if you have seen a giraffe any time in your life.
"Have you seen a giraffe already?" is asking if you have seen a giraffe as part of something happening today, such as 'this trip to the zoo', or 'this movie'.
Yes i have
"Have you once seen a giraffe"?