Both Fujifilm X-T20 and Nikon D3300 have 24.0 MP resolution sensors but Fujifilm X-T20's sensor is APS-C (23.6 x 15.6 mm ) and Nikon D3300's sensor is APS-C (23.5 x 15.6 mm ).
Since Fujifilm X-T20'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 D3300.
Another similarity between these two cameras is that both Nikon D3300 and Fujifilm X-T20 sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the X-T20 and D3300 sensor size comparison.
Fujifilm X-T20 and Nikon D3300 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.