Specify your question. Like which kind of sentence you're going to write since there are many words like that in Vietnamese.

There are many several ways to soften a tone of a question in Vietnamese, and it depends on the regions. For example, the people from North like to add "a." at the end of their question to make it softer. Anh co the giup toi duoc khong a? (Would you like to help me please?) Sometimes, "nhi?" can be used to ask someone to do something in the form of suggestion. Chung ta co the giai quyet van de nay khong nhi? (Should we try to solve this issue?). I hope it will help.

many words you can use: ạ, nhé, nhen, nha,. the saying people will use "nhé, nhen, nha" when speaking to the people with the same age or above. But "ạ" just used to the elder person.