This is the 9032nd most frequent Polish word.
sroczyńskiego
"Sroczyńskiego" is a possessive or adjectival form of a Polish surname "Sroczyński," meaning "of Sroczyński" or "related to Sroczyński."
Here, 'Sroczyńskiego' is used as a possessive form indicating ownership of the book.
Książka Sroczyńskiego zdobyła wiele nagród.
Sroczyński's book won many awards.
In this sentence, 'Sroczyńskim' is declined in the instrumental case, showing the function of the name in the situation.
Rozmawiałem z panem Sroczyńskim o tym projekcie.
I spoke with Mr. Sroczyński about the project.
'Sroczyńskiego' here is used in the genitive case, indicating the person who authored the article.