This is the 792nd most frequent Polish word.
jaką
"Jaką" means "what" or "which" (feminine singular, accusative form) in English.
Here, 'jaką' is used as an interrogative pronoun to inquire about a specific object being acted upon.
Jaką książkę czytasz?
Which book are you reading?
In this sentence, 'jaką' is used to refer to an undefined choice among several possibilities.
Nie wiem, jaką decyzję podejmę.
I don't know which decision I will make.
Here, 'jaką' refers to an identified object, emphasizing the particularity of the subject's choice.