The exact ways you say 'Which' in Polish depends on the case, gender and number (singular/plural) of the noun.
The following table is from Adam Łukasiak's Clozemaster site. I'm just putting a copy here in case something happens to that site!
You might want to give Clozemaster a whirl. The basic version is free and a great way to practice your Polish.
And if you would like to know more about "Which" because you're a bit of a Grammar fan the correct search term for Google is "Polish Relative Pronouns".
Now just before the table we need to sort out the two words for "Which" - "Jaki" and "Który"
Table explanation is below