Marie, the person asking would be best known as
a person who tries to discover information or opinions by asking people:
- Canvassers surveyed people from over 2,500 households.
- He instructs canvassers on how to elicit honest information.
a person who asks a question
possibly an inquirer or enquirer
someone who asks about something
Note that canvasser, questioner, inquirer (enquirer) have other meanings in different contexts.
a canvasser can also mean someone campaigning on behalf of a political candidate.
a questioner can mean a person who feels or expresses doubt about something.
an inquirer can mean someone that is involved in investigating incidents, e.g., a parliamentary inquiry into corruption
A good equivalent term to canvasser would be pollster as suggested by Lawrence in the answer to the What do you call a person who takes a survey? question pointed out by 1006a
a person whose job is to ask people their opinions on a subject, as part of a poll (= opinion study)
I agree with Lawrence when he points out that surveyor mentioned by OP in that question is not appropriate
To my knowledge surveyor refers to
A person who examines the condition of land and buildings professionally.
1.1 British An official inspector of something, especially for measurement and valuation purposes.
- ‘surveyors recorded the species and locations of fallen trees’
1.2 A person who investigates or examines something, especially boats for seaworthiness.
Also, in my opinion, (limited experience) surveyee given as an alternative term for John's role in your question is not commonly used.
John would be known as a respondent
someone who responds to a question or offer:
- Most respondents in the survey voiced an unfavorable attitude toward the policy.