Pentax K-S2 has a 20.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features PRIME MII processor. On the other hand, Sony A7 II has a 24.0MP Full frame (35.8 x 23.9 mm ) sized CMOS sensor and features Bionz X processor.
Another difference between these two cameras is that Pentax K-S2's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the K-S2 and A7 II sensor size comparison.
As seen above, Sony A7 II has a 2.3x Larger sensor area than Pentax K-S2. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.