Here are the most common question words in Chinese

Wh0 – shei2 / shui2 (shei2 is most common but shui2 is used by some people depending on where they are from)

What – shen2me

Where – na3li3

When – shen2me shi2hou4 (literally “what time”)

Why – wei4shen2me (literally “for what”)

How – zen3me

How about / What about – zen3me yang4

When using the question words above you wouldn’t need to use the question tag “ma” because by using a question word we already know it’s a question being asked.  You could however optionally use the “ne” at the end of a sentence using one of the question words above, but “ne” would be optional.  Perhaps similar to how is English we might say “huh” or “eh” at the end of a sentence.

However if you were asking the following question :

Do you know where the post office is ?

Asking this question in Chinese WOULD require the use of “ma” because you aren’t asking WHERE the post office is, you are asking if the person KNOWS where it is.  So the real question is “Do you know something”.

If you didn’t use “ma” at the end of the question then you would literally be TELLING the listener that they know where the post office is.  The “ma” is required to make the statement “You know where the post office is” into a question.  So you would literally say ?

You know post office located where “ma” ?

That is the word order.  You could of course use the other way of asking questions in mandarin and avoid the “ma” by saying :

You know don’t know post office located where ?

By using the “know don’t know” phrase you don’t need to use “ma”.  All “ma” questions can also be asked by stating both the positive and negative in the question instead.