It's perfectly OK to ask the OP to inform us of what he has attempted so far to solve his problem, *in a polite, constructive way*.

So many people were asking "What have you tried?" without any useful elaboration about what information would be helpful, that it was becoming rude.  As of March 2013 [that comment has been outright blocked](https://meta.stackexchange.com/questions/172758/what-have-you-tried-epidemic/172760#172760).

See the message about the block for more constructive alternatives, and consider more specific comments addressing what's lacking in the question:

> Please can you show the specific piece of code that's not working.

or even:

> Please explain what you mean by "not working".

You should always be polite - remember the rule "be nice". We're trying to "make the Internet a better place" here. In this case it's better to be a little more verbose than you might want to be as it can help to explain just exactly what information you think is missing.

However, it should be pointed out that if you need to add any (or all) of these comments then that's the mark of a bad question. Leaving these comments is hopefully the first step on getting a good question that people can answer.

If there's no effort to improve the post then it's the mark of a question that can be closed.