The part is "-かよ". It is generally an expression of mild to moderate astonishment (that can be positive, neutral or negative) - a rough equivalent in English would be something like "Aha, so...?", or by extension "Is it really ok...?" when it is clear from the context that the speaker is "rightfully" expressing his/her astonishment (like "学校サボっていいのかよ" = "Is it really okay to skip school (today)?")
The appropriate translation for the original question has already been mentioned by others, but I have to disagree with @l'électeur as I believe that under no circumstances would "Can I help you?" be an appropriate translation for "何か用かよ". If it is to be interpreted as an offer of help, it would have been said light-heartedly to a friend, and much more informal, much less polite.
In fact, it is so informal/impolite that even the "formal" version (and when actually asked, unlike in "-かよ"), "何かご用でしょうか", is at risk of coming off as being passive-aggressive (cf. "Do you want something?"). If I am to, say, offer help to a stranger, I would much prefer something like "お呼びでしょうか？" ("Do you need something?")