Both Panasonic GX850 and Nikon S6300 have 16.0 MP resolution sensors but Panasonic GX850's sensor is Four Thirds (17.3 x 13 mm ) and Nikon S6300's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Panasonic GX850's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon S6300.
Another difference between these two cameras is that Panasonic GX850'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 GX850 and S6300 sensor size comparison.
As seen above, Panasonic GX850 has a 8.0x Larger sensor area than Nikon S6300. 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.