You already know how to ask questions in French with qu’est-ce que.
Example:
Qu’est-ce qu’il fait?
Using qu’est-ce que to ask questions like this is used at all levels of language in French. Informally, you may hear something a little different on occasion:
Que c’est qu’il fait?
Que c’est que is an informal, spoken use.
In speech, il often sounds like i instead. So, now, if you heard someone say:
Que c’est qu’y fait?
… then you’ll know that what the person means is the same thing as:
Qu’est-ce qu’il fait?
[This entry was inspired by the character Claude in La Galère, season 3, episode 10, Radio-Canada, Montreal, 22 November 2010.]