It's quite a bit interesting question.:)
1) "어떻게" can be translated in two ways in English,
literally it can be "HOW", but sometimes it can be "WHAT".
For example,
What's your address?
"주소가 어떻게 됩니까" is more natural than "주소가 무엇입니까?"
What do you think of my new car?
"내 새차 어떻게 생각해?" is more natural
How's the weather there? or What's the weather like there?
"거기 날씨 어때요?"
What would you do if I said no
"내가 안된다고 한다면 어떻게 하시겠습니까?"
etc...
As you can see it, there are no rules in here, just should get used it.:)
2) Yes, you are right.
You can start with "how do you(I/Koreans) say A in Korean" or
"What do you call A in Korean"
3) "말해" and "말하죠" are the same meaning except the level of the politeness.
As CHL said above, "말해" can be used to a friend or younger persons while "말하죠" is a polite version of "말해".
Looking at the politeness of it,
"어떻게 말해야 합니까?" (very polite)
"어떻게 말해야 하죠?(or 말하죠?)" (a bit polite)
"어떻게 말해?" (between close friends)