can i ask question on a particular product by adding the hashtag #wip for example

Nope. See my reply here:

@pugson Yep, but i think Marc said it should work that way. maybe its a bug or still wip.

Right now only the owner of a product can tag a question. The reason is that product hashtags are scoped to the user. That way different people can use the same hashtag without a problem. Useful when using abbreviations and acronyms.

I might make these hashtags system-wide and/or allow you to manually attach a product to a question.