More colloquially,
어떻게 그걸 말해요.
전 말못해요.
어떻게 말해야 할지 모르겠어요.
In Korean, we usually don't use 당신 except between husband and wife or when you show some distance as well as some hostile. So you should not use the expression 당신(even though its original meaning is you and it is an honorific term). But don't be confused that when we argue or quarrel with someone, we should show some level of respect so we use the term '당신' but it never means 'dear and lovely you' but just 'you, sir'.
