は何人ですか

how many people are there?

→ は
phrase Rare #19,963
how many people are there? Used to ask how many people are in a group, class, family, population, or other specified group. The topic before は is what is being counted.
JA: あなたの家族は何人ですか。
EN: How many people are in your family?

この島の人口は何人ですか

How many people live on this island?

今年あの学校へ入学できた生徒は何人ですか

How many students were admitted to that school this year?

乗客は何人ですか

How many passengers are there?

子供は何人ですか

How many children do you have?

生徒人数は何人ですか

How many students are there?

乗客は何人ですか

How many passengers are there?

君のクラスの生徒は何人ですか

How many students are in your class?

人数は何人ですか

How many people are there?

フランスの人口は何人ですか

What is the population of France?