"How to draw a correct graph?" This is what it sounds like to me, though I can see the similarites.
I really do think so too. "grafik yang benar" means "a correct graph" I guess. May be the appropriate English translation for this sentence is "Bagaimana cara mengambar grafik dengan benar?". Someone correct me please if it is wrong.
"Bagaimana" equals "what" now is it?
In thus case, yes. You have to take the sentence in conext. Using "what" in this type of sentence, which discusses a skill or action, would sound weird in b.Indo, but bagaimana makes sense.
Shouldn't the Indonesian sentence be /Bagaimana cara yang benar (untuk) menggambar grafik?/
The sentence Duo provides is /Bagaimana cara menggambar grafik yang benar?/ and that syntax makes /benar/ modify /grafik/ instead of /cara/.