Xin lỗi cho tôi hỏi

You can, but it's ambiguous. It's better to add 'cho tôi hỏi' so people know you have a question and aren't just apologizing for bumping into them.

It's neutral. It's never 'wrong,' but using kinship terms like 'em' or 'cháu' makes you sound much more like a local.

If they look roughly your age or older, use 'anh' (male) or 'chị' (female). If they are much older, use 'bác'.

Yes, you can just say 'Cho hỏi...' or 'Xin hỏi...', but these are slightly less soft than the full phrase.

A full bow isn't necessary, but a slight nod of the head while saying the phrase is a very polite Vietnamese gesture.

For that, use 'Xin lỗi, cho tôi đi nhờ' (Excuse me, let me pass through) instead of 'cho tôi hỏi'.

Yes, it's a very common way to start an inquiry in a formal or semi-formal email.

In the South, people often say 'Làm ơn cho hỏi...' which is equally polite and very common.

Absolutely. It's the most polite way to get their attention for a question about the menu or the bill.

Say it slightly louder and add 'Anh ơi' or 'Chị ơi' at the beginning: 'Anh ơi, xin lỗi cho tôi hỏi...'

Yes, it's the standard way to ask a question during a presentation or meeting.

In this context, it functions more like 'Excuse me' in English, acknowledging the interruption.