February has a variable number of days. לְפֶבְּרוּאָר יֵשׁ מִסְפָּר מִשְׁתַּנֶּה שֶׁל יָמִים
That sounds weird, but along the same lines I think "How many days does February have?" could be acceptable.
It's not correct English grammar. You could (Hebrew translation aside) say: how many days does February have?