"what/which date do you want me to start?"

Question

I was talking with a prospective hiring manager, and I wanted to ask him what date he wanted me to start working for the company; and I wanted to know the latest possible date because I wanted to take some time off between jobs.

So for the first question, I was wondering which one of the following sentences is correct:

1. what date do you want me to start?
2. which date do you want me to start?
3. what date do you want me to start on?
4. when is your preferred start date?

To ask for the latest start date, which one of the following sentences is correct?

1. when is the latest start date that you are comfortable with?
2. how late can I join/start?

Answer 1

"what" describes an open set, "which" describes a closed set. To put it simply, "what" is more specific than "which".

"which" refers to a closed set, if there is a limited number of choices as the answer. For example, imagine that there are three books in your friend’s hand, and you want to know the best book out of them. Then you can ask, “Which book do you like the most?” Here, the answer will be one of the three books.

So in this case, "what" or "which" both can be used in the first and second question, as you want the latest possible date/date

What/which date do you want me to start?

So sentence (1) and (2) can be used. Im Sentence (3) the "on" is not neccessary. Sentence (4) can be used as well, but the first two sentences are more preferred. - 1st question

Sentence (1) is the best one out of the 2, as sentence (2) might sound like you want to slack (even though you're not), but otherwise sentence (1) is more polite towards the manager.