Breakdown of Рукопись, которую он сейчас читает, уникальная.
он
he / it (for a masculine noun) / it (for a neuter noun)
сейчас
now
читать
to read
который
which / who / that (relative pronoun)
Questions & Answers about Рукопись, которую он сейчас читает, уникальная.
Why is it которую and not которая?
The word которую links back to the feminine noun рукопись (manuscript), so it takes a feminine form. But inside its own mini-sentence ('which he is reading'), the manuscript is the direct object—it is the thing being read. Because of this, it has to be in the accusative case, making it которую.
How can I tell that рукопись is a feminine noun?
Why are there commas around которую он сейчас читает?
In Russian, relative clauses (descriptive phrases starting with words like 'who', 'which', or 'that') must always be separated by commas. You need a comma to open the clause before которую and another one after читает to close it before finishing the main sentence.
Why is уникальная just sitting at the very end of the sentence?
If you remove the relative clause in the middle, the core sentence is simply Рукопись уникальная. (The manuscript is unique). Russian doesn't use a linking verb like 'is' in the present tense, so the sentence just pairs the subject right with its describing adjective in the nominative case.