Learn Polish: On chce, żebyś znalazła raport wśród tych dokumentów. - He wants you female to find the report among these documents.

This is the standard way Polish expresses wanting someone else to do something. You use the word żeby followed by the past tense form of the verb, which is also called the l-participle. Because the speaker is talking to a woman, we use the feminine form znalazła.

Where does the "you" come from if the verb is just znalazła?

The "you" is hidden in żebyś. Polish takes the -ś ending, which indicates "you", and attaches it directly to the word żeby. You cannot attach it to the verb here to make żeby znalazłaś — the personal ending must go on żeby.

What case is being used for tych dokumentów?

That is the Genitive case. The preposition wśród, meaning "among", always forces the words that follow it into the Genitive. Since there are multiple documents, we use the plural forms: tych for "these" and dokumentów for "documents".

Why is the perfective verb znalazła used here instead of an imperfective one?

Finding a specific report is a single, completed action, which requires a perfective verb. If he wanted her to "look for" the report, which is an ongoing process, the sentence would use the imperfective equivalent: żebyś szukała.