To Inspect
To Examine, To Check
する verb
You examine the problem. In order to do this, you need to inspect it or to examine it. And if you're inspecting people like this, you're probably the police.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
ほら、あそこで検問しているよ。
Hey look, the police are examining people over there.
警察が私の車を検問している時、ドキドキしました。
While the police were inspecting my car, my heart was racing.
成田空港の検問所で検問している警備員の中には、トレーニング中の警備員もいます。
Some of the security guards who inspect people at Narita Airport's checkpoints are undergoing training.