何〜か【なん〜か】

何 (read なん) with a counter and か makes an indefinite number: "a few", "several", "some". The counter is whatever the thing normally takes: ひと人 for people, かい回 for times, さつ冊 for books.

The number is small to moderate, never "a lot"; for that, use たくさん or なんにんも何人も.

何人か or 何人

Without か, 何人 is a question: "how many people?". With か it is a statement, or a yes-or-no question.

Where it goes

Like other numbers, it can stand after the noun and its particle, or before the noun with の. Both are normal.

The counter keeps its usual sound changes: なん何ぼん本か is なんぼんか, なんかいか何回か is なんかいか.

何〜か or いくつか

いくつか also means "some" and needs no counter, so it suits things you would count with つ. With a counter, you say exactly what kind of thing you mean.