This is the 10469th most frequent Polish word.
czytaniu
"Czytaniu" means "reading" (dative or locative form of "czytanie").
Here, "czytaniu" is used in the dative case after the preposition "na" which indicates the focus area, translating to "on reading".
Byłem skupiony na czytaniu instrukcji.
I was focused on reading the instructions.
In this context, "czytanie" is derived from the verb "czytać" in its gerund form, denoting the act of reading itself as part of the sentence structure.
Zajęło mi sporo czasu przyzwyczajenie się do czytania po angielsku.
It took me a lot of time to get accustomed to reading in English.
In this sentence, "czytaniu" is used in the dative case as part of the prepositional phrase "przy czytaniu", meaning "with reading" or "during reading".