Why do some Polish surnames end with ‘ski’ or ‘ska’?
The suffix ‘ski’ is quite simply the equivalent of ‘from’ or ‘to come from’.
So for example, the name Jablonski indicates that historically the name was given to someone from Jablonka / Jablonica. Itself stemming from the word jablon (apple tree), or the diminutive form jablonka. Similarly the someone coming from Kowalew / Kowalewo might well have the common Polish surname Kowalewski (meaning someone from the place of the smith). Which itself originates from the word Kowal (meaning Smith in English).
A Polish surname, which ends in ‘ska’ rather than ‘ski’ just means that the person is female. ‘Ski’ is the male version.