Learn Hardcore Japanese: uketuke de pasupooto wo misemasita. - I showed my passport at the reception desk.

で marks the location where an action takes place. In this sentence, the action “showing your passport” happens at the reception desk. In contrast, に would mark a destination (e.g., “going to” somewhere) or a point in time, not the place of an action.

Why is を used after パスポート?

The particle を identifies the direct object of a transitive verb. Here, パスポート is the object you’re showing, so it takes を before the verb 見せました.

Who is the subject of this sentence, and why is it omitted?

Japanese frequently omits the subject when it’s clear from context. In 受付でパスポートを見せました, the implied subject is “I” (the speaker). Since you know who is doing the action, there’s no need to say 私 or 僕 explicitly.

Why is 見せました used instead of 見ました?

見せました is the polite past form of 見せる (to show). 見ました is the polite past of 見る (to see). Because you actively show the passport to someone else, you use 見せる rather than 見る.