Both Canon 750D and Nikon D5600 have 24.0 MP resolution sensors but Canon 750D's sensor is APS-C (22.3 x 14.9 mm ) and Nikon D5600's sensor is APS-C (23.5 x 15.6 mm ).
Since Nikon D5600'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 Canon 750D.
Another difference between these two cameras is that Nikon D5600'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 750D and D5600 sensor size comparison.
As seen above, Nikon D5600 has a 1.1x Larger sensor area than Canon 750D. 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.