I feel like I’m constantly looking up what questions were asked (and exactly how) on the 1940 census. Well, a copy of the blank schedule answers that.

From wikipedia: https://upload.wikimedia.org/wikipedia/commons/7/76/1940_census_form_large.jpg

And saved forever here

Some variables only on the sample line:

• A second copy of your name
• Mother and father place of birth
• Native tongue
• Veteran status
• Social Security Q’s
• Age at first marriage and number of children ever born

Earnings, education, occupation are all asked for all enumerated people.