English question for days

Sure.

You can leave out "of the week" and not lose any meaning, especially if the period of discussion has been signalled already e.g.:

Person A: I only work part of the week.
Person B: Which days do you work?
Person A: I work Mondays, Wednesdays and Fridays.

Hi all,
thank you.
roger, you look so cute today.

You got something against Rats, Jane?

Yes roger,I am afraid of rats and cockroaches.But your rat is very adorable.

It is probably better to start the sentence with "What." "Which" generally begins a dependent clause.