which is correct? How much IS a dozen of donuts? OR How much are a dozen of donuts?
1) The standard term is "a dozen donuts" (not "a dozen of donuts").
2) The question "How much is a dozen donuts?" could mean one of two things:
a) How many donuts make up a dozen?
b) What does a dozen donuts cost?
3) American English usage is fussier than British English with regard to number agreement between subject and verb. In British English, both forms of your query sentence would be acceptable (provided the 'of' is omitted), whereas American English usage would usually prescribe "How much is a dozen donuts?"